I'm happy to pay for other people's kids to get good educations because I don't want to be surrounded by idiots. Just because you don't have kids doesn't mean you're not living in the same society.
In some fantasy world where enough people act selflessly for this to be a theoretically significant issue, such concerned folks can just donate sperm/eggs. We already have a mature industry for handling that.
Fact is the vast majority of humans reproduce and will continue to do so, no matter how many comments on HN try advocate otherwise.
But I'm an optimist; go childless, we've got headcount more than covered here on Earth! Don't let society make you feel guilty or selfish for not throwing more fuel on this raging inferno of a dumpster fire.