> 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.