So, I'm familiar with the arguments in this thread - children as extra workers in rural areas, carers for the elderly, etc. And it makes perfect sense in terms of logic.
BUT are people really that logical? And is this really applicable across every single culture and nation on Earth? Because birth rates have declined everywhere. Some places much sooner than others, sure, but everywhere. Are rural peasants in China, and working class Brits, and Favela Brazilians, and Upper class Germans, all sitting there thinking... well, I can only afford to put one child through university in 20 years time, and the state will definitely provide for my care in 60 years time, so one child it is? It just seems so far removed from how the vast majority of people think, in my experience. Not to mention, many declines seem to have occurred before widely available birth control... going off one example in this thread, how were working-class Londoners deliberately restricting the number of children they were having in the 1900s? Did everyone just stop having sex?
I don't really have a coherent alternative, but the conventional explanations just don't seem to fit with reality to me.