To answer the title question: I don't know. It's not clear to me if anyone knows the answer to that question for certain. It's quite likely that Armstrong (yes, first human on the Moon Armstrong) did kill people, and yet there's no clear (public) record of it. Very few sources even seem to want to report it, only noting slightly euphemistically that he flew combat missions in Korea, and then they rush off to his later, cleaner exploits.
That's kind of weird. The actual violence tells us something about Armstrong, but the whitewashing of his background arguably tells us more about ourselves.
To spell it out clearly, he was mostly involved in ground attack flights, for example bombing anti-aircraft guns (which would likely have killed the people firing those guns), so that later bombers could pass by unimpeded (and possibly kill more people with their own bombs). This is what Neil Armstrong did before he became an astronaut.
I don't think this is the defining activity of his life, if such a thing even really exists. We all mainly know him as the Moon guy, but we also get that this wasn't his whole life. Most people would think of him also as a scientist or pilot, and those who've done their homework would be more specific and call him a naval aviator, test pilot, engineer, and academic. Some might focus on his family life, or his religion, or his media presence. But it doesn't take that much thought to go beyond purely "Moon guy". So why the resistance to also giving him the title of "someone who has probably killed people"?
This is something that's bugged me about many astronauts. Quite a lot of them have military backgrounds, and more than a few have shot people. In most sane professions, that's something that keeps you from getting even the first interview, and yet NASA considers it a virtue instead? We put these people up on pedestals and expect kids to regard them as rolemodels. (Are we hoping the kids will never find out about the violence? Or that they will?) When the first astronauts were hired, it was widely considered damning that most of the early ones were having a lot of sex with a lot of people (oh noes!), and yet not damning in the least that they might have ended someone's life on purpose. That's a pretty fucked up set of priorities.
I've responded to this by doing what any sane, well-adjusted individual would do, and spent several days scanning through every single astronaut/cosmonaut/taikonaut profile page on wikipedia (plus other sources, notably spacefacts.de, where greater clarity was needed) to build up a spreadsheet that categorises all of them by the level of violence they're known to have embraced. Below is the google docs version of that.
The first column with the H's denotes whether they're known to have killed non-human animals, mostly through hunting/fishing. I had a hunch early on that there might be a link between that behaviour and violence against human animals.
The second column gives the person's violence level, on a scale from 0 to 3. 0 indicates no known violence; 1 indicates military employment, with no known actual violence; 2 indicates participation in violent activities, but uncertainty about whether this actually killed anyone or not; 3 indicates definitely actually killing someone.
The fourth column supplies a couple additional notes, clarifying context.
This analysis is mostly only good for spotting major incidents of publicly documented violence. Statistically, it is probably missing all manner of bar brawls and sexual assaults, and it's not inconceivable that someone on this list could have covered up actual murders. But I just don't have evidence for most of that, so I only go with what I can confirm with reasonable certainty.
A separate sheet, in the same format, records space tourists separately from the working spacecraft crews.
There's a lot to process there, even summarised down to this table, so I also put columns 2 and 3 in graph form:
Violence level 1 deserves quite a bit of explaining. It makes the most consistent line in the graph, especially in the early years. The military origins of human spaceflight (and spaceflight in general) are no secret. Very few nuclear-armed missiles can't trace their origins somehow back to the V-2, and most human-carrying rockets were either originally weapons, or were designed by the same people who also designed weapons. The governments that funded putting things (human or otherwise) in orbit knew very well that they were mainly doing it to cover up development of military satellites and nuclear bomb launchers. This intention was naturally kept secret at the time, which is why the cultural narrative about spaceflight is so distorted, but it's well-established historical fact today, if you take the time to learn about such things. (I'm enjoying Teitel's Breaking the Chains of Gravity, if you're looking for an introduction to the topic.)
This was also the only real reason that military pilots were chosen to be the first astro/cosmonauts. The same essential skills could be found among civilians, especially during the earliest spam-in-a-can phase, when the spacecraft required no pilot, and the human inside was really just a big guinea pig. So why insist on military crews? Because they'd be working with classified military technology all day long, and Dwight Eisenhower personally decided it would be simpler for NASA to only recruit crews who already had established clearance to work with military secrets. The Soviet government made a similar choice, and it seems China has more recently done the same, all for pretty much the same reason: Military space travellers aren't extra-skilled, they're just less likely to sell your secret weapon designs.
It is true that military pilots are more likely to have fast jet experience, but it turns out that this experience doesn't necessarily translate to spacecraft flying skill any better than other types of piloting experience. And as spacecraft got bigger over time, and crews expanded beyond just the pilot, they started needing people with completely different skill sets, and that's where we start to see the military test pilot fall slightly out of favour. The Soviets were the first to embrace civilian crew, and today many of the most experienced Russian cosmonauts have no military background at all. The US followed along later, mostly during the shuttle years. Yet despite a growing list of purely civilian spacefarers, that line of military ones remains pretty solid too. And it's still because rocketry is considered, first and foremost, a military area of interest, with secrets that need to be kept from "tha baddies".
Violence level 1 is also complicated, because I certainly wouldn't say that everyone at that level is definitely equally violent. It encompasses everyone from those who are trained and willing to use some awful weapons, but simply never got the opportunity to use them, all the way to those who are technically military employees, but whose work is clearly non-violent and may never even contribute to violence, such as medical professionals. It's tricky to find a neat dividing line between the two extremes, though. A test pilot or weapons manufacturer may never actually use their weapon on anyone, but they are clearly developing it so that someone else can use it to kill people later on. So are they morally suspect or not? Senior commanders of military units may never go anywhere near the combat area, but it's hard to argue that ordering people's deaths at a distance is an ethically positive thing. And even logistics support people are indirectly responsible for deaths, when the food they deliver gets eaten by the guy who will go off to kill people. Delivering food clearly isn't violent, and yet if that food wasn't there, the guy doing the killing couldn't have hung around long enough to kill anyone, and the logistics people know that, which is why they deliver the food. It wasn't a coincidence that they fed the guy, it was part of a plan to kill people. So it's hard to draw a very clear, solid line between "good" and "bad" military employees. I think it's much simpler to view the whole military as a killing tool, and to be at least suspicious of anyone who works as part of that tool.
But that doesn't make my astronaut list that much clearer, which is a slight annoyance to me.
Violence level 2 is something I'd really rather not have, because it's ambiguous and imprecise, but unfortunately that's the best level of detail currently available to me. I'd much rather know for certain who is definitely level 3, and who can drop back to level 1. Unfortunately, around the time of the Apollo program, astronaut biographies started getting sanitised. Where fighter pilots had previously been very eager to boast about the people they'd killed, competing as if it were a sport, that publicly went out of fashion, and so it was no longer reported as clearly. We know for certain that John Glenn shot down 3 planes, possibly representing 3 dead pilots, in addition to the unrecorded number of people he killed in ground attacks. (That distinction in how much they valued - and thus recorded - air kills versus ground kills is noteworthy.)
At some point, the US military public relations people realised that a lot of the public didn't want to hear the gory details of war, didn't want to know how the sausage was made, and perhaps there was also a counter-intelligence argument for not boasting your war successes too openly. And so every published combat record from the Vietnam War onwards merely reads that the person took part in "combat operations" or "flew combat missions". That euphemism could mean anything from blowing people up, to helping others blow people up, to flying in circles aimlessly for hours, just so long as it's done within an area where fighting is happening. So, for my purposes, I'm stuck with level 2; some people put at that level may never have done any direct harm at all, but at the very least, we can say with some certainty that they made an effort to try to kill people. That willingness to be violent, I think, counts for something.
(I also wonder if there's something similar with column 1, the hunting thing. Has hunting become less popular than half a century ago? That would fit increasing urbanisation trends. Are animal-killing astronauts as common as ever, and the PR people just keep that off their official profiles now? Or describe it with euphemisms that I'm not spotting, like "hiking" or something? Maybe. I still think there's a general inclination to kill, whether humans or non-humans, that should produce a correlation, but the unexpected big void in column 1 makes that hard to check. Good news if it's a realistic void, at least.)
With that all clarified (I hope?), I'd like to point out a national distinction: Almost all the level 2's and 3's are American. It's possible that the Soviets/Russians simply never admitted that some of their cosmonauts had combat records beyond the few from the Second World War, but I think that's unlikely. The far more obvious explanation is that the Soviet Union didn't go to war nearly as often as the United States. From 1945 to 1990, the Soviet Union may have supported or encouraged or sponsored conflicts, but very seldom participated directly in any major way. The decade-long Soviet-Afghan War was the one big exception, and it is a little surprising to me that no cosmonauts seem to have emerged from that. Post-Soviet Russian conflicts have been much more numerous, but generally less intense and less persistent, mostly related to resolving post-Soviet borders by force. The Americans, on the other hand, have been incredibly violent for most of the last 60+ years, with heavy involvement in some of the biggest contemporary wars. Korea. Vietnam. The Gulf War. The US wars in Afghanistan and Iraq. And always lots of smaller conflicts in between as well, with the possible exception of the Carter years. The Syrian civil war is probably the first time since the 1940s that the Americans and Russians have had comparable participation in the same conflict. Beyond the three main spacefaring countries, the most violent source of astronauts is France, with some noteworthy anomalies from Belgium and Vietnam.
Analysing and explaining all of this is a huge, textbookworthy topic of its own. My sole point for now is that it shouldn't be surprising if few Soviet/Russian military pilots had ever actually seen combat. This is even more true for Chinese taikonauts, as China has been remarkably peaceful for decades.
I think it's also important to avoid excessively monolithic thinking.
Not all Americans (or Russians or Chinese) are the same, not all NASA administrators are the
same, there has to be some room to consider individual and local quirks.
One interesting example is that it was NASA that convinced the Russians
not to take any guns to the International Space Station, and not the
other way round.
The implications of this are worth debating. Does it mean that Americans are the Klingons? That soldiers are or are not responsible for their wars? I don't think this small data set is enough to be sure of too much, but it does get you thinking, I hope. The main reason I bring it all up here is to illustrate one point: Combat experience is not needed for good astronauts. Killing people doesn't make you handle spaceflight any better.
And so it's weird that NASA has evidently chosen to hire so many astronauts on the basis that they've killed before. It means that someone once sat down and wrote that in as a job requirement, a positive trait for potential recruits to have. I doubt they worded it exactly that way, but they didn't do it that many times in a row, hiring several dozen candidates with combat experience, purely by coincidence. If nothing else, they haven't viewed it as a negative trait.
To be clear, I'm not saying all of the non-military spacefarers are uniformly and perfectly good people. Some, I'm sure, are dicks. But they're dicks who haven't killed anyone, which is a better starting point. As an example, Schmitt's position as first purely civilian American astronaut is
spoiled a little by his current deeply unscientific views on global
warming, which he insists on publicly espousing. That's not really a
violence-related thing, but it does definitely dent his reputation - but less than if he'd shot someone, I think. Of course, some really are great; it's hard to criticise my two favourites, Ride and Jemison, for example. They weren't just non-violent, they actively worked to make the world a better, safer place. Jemison is still at it today, and Ride's legacy will hopefully continue on. Even some of the level 1's seem to have a lot of genuinely positive traits going for them; I'm fond of Hadfield and Cristoforetti, for instance, to the point that I strongly hope they wouldn't ever have pulled a trigger, if they'd been told to. But realistically, I have to concede that they probably would have. And I think that's one of my big conclusions here: If you join an armed organisation that deals primarily in violence, then your choices are automatically suspect to me. Either it means you accept violence, which is bad, or that you're so blind to violence and its consequences that you really shouldn't be trusted with anything more dangerous than a plastic spoon. If you actively oppose violence, your alternative solutions may not work, but at least you've chosen not to kill anyone.
I'm not certain I can draw anything else much more conclusive from this relatively surface-level analysis. I think there's enough unsettled about all of this to warrant a full PhD thesis, if anyone is looking for a topic.
Since I don't like ending on a hanging thread, I do have a couple little notes on smaller things I picked up on while writing this:
My recording of Joe Walker versus James Halsell is worth explaining a little. Both were involved in fatal vehicle accidents, but I've marked Walker as level 1 and Halsell as level 3. Walker's collision appears to have been a genuine accident, certainly not something Walker wanted or could have predicted or controlled. Halsell, on the other hand, intentionally drove drunk, knowing full well what that entails. That's not anyone's fault but his own, and if that caused him to speed, or if he would normally speed while sober too, then the blame still lies with him.
Linnehan's involvement in the Marine Mammal System is as laughable as it is tragic. What these veterinary quacks do to dolphins and sea lions is simply cruel (whether you accept war or not), and if we're supposed to value fighting in wars (which I clearly don't) then surely this should be viewed as a cowardly technique anyway.
There's a fairly unsurprising gender split, with relatively more women in level 0 than men, and none confirmed in level 3.
The space tourists, even less surprisingly, are all level 0. I did briefly wonder whether Shuttleworth might have been conscripted into the South African army (I wasn't sure whether he was young enough to have missed the conscription years), but it's apparently fairly widely known that he skipped the country to avoid that. Elon Musk did the same, which is part of the reason it disappoints me that he now wants to feed rockets to the US military. That's kind of hypocritical.
Mark Kelly is an idiot. After an assassination attempt on his wife, former member of Congress Gabrielle Giffords, the two of them remained pro-gun. Kelly himself has dropped bombs on people (I have him at level 2 above), but it's not unheard of for the physical distance between pilots and their targets to lend them some very unrealistic emotional distance. They don't often actually watch their victims die, from way up in the sky. But you'd think that when 6 people die, including a poor fucking little 9 year old girl, and his own wife is horribly injured, along with a dozen others, then surely he'd get it? Surely he must, however briefly, have drawn the connection between what he did and what Loughner did? If he did, then it was a very weird connection he drew, simply calling for the mythical "bad guys" to have their gun access restricted, while he and the "good guys" kept theirs. (I'm pretty sure there's a fair bit of psychology or cultural anthropology research that could be done on these people.)
This has been a pretty grim, disheartening post to research and write, so let me end on Leland Melville's official astronaut portrait. It's hard not to be happy about this.