My response is here. I didn’t like kids, except in theory. Children were just fine as long as I could hand them off to their parents when I’d had enough. It’s fascinating to see what a change I’m going through now I really am a parent. It’s hard to explain.
King Rat seems to have hit the nail on the head, as far as the reasons industrialized nations have a reduced birthrate compared to less-industrialized nations. When it’s a matter of survival, you have kids. When children are not part of the survival equation, it’s just as easy to say no, especially since the invention of many different means to avoid parenthood (mainly contraception).
Also, it’s only recently been possible to avoid having kids. In the past, if you didn’t want kids, you’d pretty much have to remain a spinster (I hate that word) or a bachelor. I can easily imagine how distressed women were in the past when faced with the prospect of bearing a child every one or two years until their bodies wore out and died.
Looking back over the archives of a really cool website that details the lives of everyone in a small town right by the place where I grew up, it’s interesting to see that there were quite a few men and women who chose to remain unmarried. They contributed immensely to their families and to the community in general, tended to have a bit more money and were better educated. I hypothesize that if a genetic factor for not wanting to have kids exists, it’s a beneficial one. More adults caring for fewer kids= more resources (and hence, more likelihood of survival) for those kids.
Another possibility (actually, my guess is that it’s probable) is that many of those unmarried people were homosexual, but such a thing could never be admitted in proper Victorian society. In that case, too, the nieces and nephews benefitted from their relatives’ childlessness.