I mostly don't downvote anti-having-children(?) comments (I just ignore them), but I think most of them are counter-productive because, as others say, the desire to have children is ingrained to a lot of people, so not having children is a really tough sell. In light of the climate emergency we're facing, it almost sounds like deliberately advertising a wildly unpopular plan, detracting from other actionable plans with much higher chances of being accepted.

And the (not always, but frequent) I'm-holier-than-thou-because-I-transcended-ape-instincts vibe doesn't help.