That's all fine and well as an internal idea why you don't want to have kids, but when anti-natalism became a "thing" that started attracting like-minds it became another group of insane people online pushing their anti-society ideals

And lastly, mostly, the idea quickly attracts people who just hate children and that's something we need to fight with all our might as a species.

You said that anti-natalists dislike when their beliefs are challenged, but the first thing you do is concede that point and start talking about your personal perspective on the history of anti-natalism. I'm trying to present as close as you can get to a logically-valid anti-natalist argument, but it seems like your personal experience with people you perceive to be anti-natalists has tainted your ability to engage with that perspective. Claiming that an idea attracts crazy people is just an anecdotal ad hominem, not an actual issue with the idea. If you want to talk about why you perceive it to attract crazy, antisocial child-haters, then first establish that that is the case and suggest what it is about the idea which makes such an attraction dangerous. Fascism isn't bad because the worst people rally around it. The worst people rally around it because of the things which make it bad, such as the ease with which those in power in a fascist state can exploit the weak for personal gain.

It appears, to me (though it is ambiguous, so let me know if I'm off-base), that you believe that the biggest danger of anti-natalism is in the potential of population decline. If a significant portion of the population agreed with an anti-natalist argument, such that they actually did believe it was morally irresponsible to have a child, I contend that the problem which must be solved is not their exposure to anti-natalism, but the things which caused it to be a convincing argument, namely the fact that the future of a child born into this world is a deeply risky bet, due to the reasons I've listed and more. I don't think that people taking a rational cost-benefit analysis of a situation is a problem. The problem would be the situation.

In fact, it seems like (again an implication, so correct me if I'm wrong) you are concerned that an anti-natalist would try to forcibly prevent people from having children, but such an action would increase the suffering of those alive, and the actor would be morally culpable for such an act. As such, if you are, instead, suggesting that anti-natalists believe in forced sterilisation or otherwise, then I think that it might not be the anti-natalists projecting their own problems onto the world.

All that aside, I still think it's a narrow perspective, because unless you know something I don't, we don't know if there's an alternative to existing and experiencing things, I mean... you're going to die, and you will be dead forever. If you're a teacher you should know the basic ideas about the universe and how everything appears to be probabilistic in nature. Eventually, after all the stars die and a number of years pass that make time meaningless, it will eventually all happen again. In some form or another. The universe will always be experiencing itself, not having kids now just means that conscious experience is going to express somewhere else, some distant configuration. It happened once already, and few things in nature are singular.

As an earth and space science teacher, why yes, I DO know some things about the cosmos. For instance, I know that the "big bounce" theory (everything repeating) is only one of many potential interpretations for the future of our universe, and is by no means the most popular among astrophysicists, since it appears inconsistent with a universe in apparently-accelerating expansion. Far more likely is heat death or the big rip, which would make all effort to come before existentially meaningless, unless some method of information transfer outside of our universe or beyond our current understanding were to be achieved. It's a good thing that none of us will be around to experience those eventualities. If you'd like to chat about existential nihilism, absurdism, or other concerns, I'm happy to do so, but I don't perceive them to be particularly germane to the argument at hand, unless you're trying to use a nihilistic argument to tear apart a fairly common position among nihilists. Utilitarianism itself is, ultimately, a response to the lack of meaning in the cosmos, and is an attempt to ascribe meaning by our own, subjective definition, so of course it's human-biased, but it can be applied evenly, even to animals, which seems to be a primary concern for you.

and if we're going to go out quietly into the night, we should do it with the least amount of harm, and I would rather we put that energy into taking better care of the people we already have.

That is... Exactly my point. Are you sure you are disagreeing with me? We need to be actively taking better care of the world, so that no one need feel afraid of bringing a life into this world, only for it to experience unspeakable suffering.

Do you know for sure if you're actually reducing suffering? Or just reducing your own guilt? For all we know, this is as good is as it gets.

Such a thing is fundamentally unknowable, but our definition of suffering is fairly consistent, and of course It's all about personal moral culpability, because that's the whole idea of morality. If you're going to take so many nihilistic and moral relativist stances, I don't see why you're so concerned with population collapse or animal welfare.

We don't know if the alternative to this is better, odds are it isn't, we don't know if you are actually deciding if you're bringing in a new life or only changing the shape of your own conscious experience in this universe. We don't even know if you have a choice at all, and are not just post-hoc rationalizing decisions you've already made.

While it is fair to attack the postulates of an argument, this is not, in my opinion, a particularly compelling argument. Sure, I assume that not creating a life does no harm, but to say "ooh, free will might be an illusion" doesn't actually negate my point, because, at worst, this means that it doesn't matter whether you're anti-natalist.

[a] crustacean that gets cronched by some predator or a primate who suffers horribly and dies after her family is murdered by another tribe.

My argument does not apply to animals in a state of nature, as those animals are not reasonably expected to have responsibility (If I were to learn that a species of animal did, in fact, have sufficient mental capacity to understand existential philosophy, then I would probably be having this conversation with a dolphin, rather than a lemming). Humans are the active cause of the current mass-extinction event, and we have the wherewithal to potentially stop it. That is, from my perspective, a moral imperative. Humans are the cause of a great deal of suffering, both human and among other animals, and one of my precepts claims that suffering can have a net-negative effect on the value of life. Another precept enjoins us to act, as the failure to act constitutes negligence. Do i believe that we must all stop procreating? no. Do i believe that there are cases in which it is actively irresponsible and negligent to bring a child into the world? Absolutely, yes. Do I think that I have a moral responsibility to stop people from fucking? No I do not. Do i believe that everyone must be educated on the responsibilities, risks, costs and benefits of parenthood, so they can be informed when they consent to engage in procreation? Yes. Do I think I have a moral responsibility to make the world a better place for the inevitable products of the aforementioned fucking? ABSO-FUCKING-LUTELY