Another thing I've learned is that far too many parents take the statement "I don't want kids" as a personal challenge to moralize and condescend to people without children.
Na, I think it has more to do with either projecting ones own wishes onto somebody else or maybe even talk somebody down so that you can feel better if you don't are completely happy with the current situation.
I find it much more interesting to ask why somebody wants no kids. That gives much more insight into the person's mind than when you try to persuade them with your own experiences and produces much better followup talk opportunities.
Anyway, I'm curious what you think it might be evolutionary advantageous. On the face of it, if others have less kids, that would seem advantageous to your own kids.
What, aside from never making any decisions (which is a itself a kind of decision), can you do other than trying to make the best decision you can right now?
The honest to goodness answer here is that you can let other people make decisions for you, and it is the desire to make decisions for other people that prompts this argument.