> It's always funny how many people think that the only font of altruism is taking care of children who have your DNA, like that's some kind of selfless act

This is a strawman position in my opinion. I don't think there's that many people who think they're carrying out some selfless act by having children. It's simply biologically true that the children you'll probably have the easiest time raising are your own and, assuming we want to continue as a species, we do need people to have children. It's fine to have them, fine to not, neither side has some moral high ground.

It’s uh, historically proven, so to say.

I think what usually gets mixed up is how the responsibility works, and biological children sit at the overlap.

The thing I most crucially remember about my son being born is that it felt downright easy to simply dive into all the things I would now be doing: because there was no one else. I either got it done or it didn't get done.

Someone else's kids on the other hand there is a choice: their parents.

It's not absolute IMO but you also see it echoed by working too: when it's your job, it's a lot easier to simply go "right I need to handle this" then when it's not.