> Birth rates are extremely low even in countries that paid parents to stay at home with kids and generally have good work culture.
I'll still bet that there's a significant career opportunity cost to leaving the workforce for a while like that.
> You would also expect birth rates to be lowest among people working 2-3 low-wage jobs, which is also not true.
If anything, aren't these the people for whom the opportunity cost is lowest? A gap on your "resume" after "McDonald's fry cook" to care for your kids doesn't require much explanation when you later apply for "Starbucks barista". If on the other hand you're a lawyer, maybe you didn't make Partner.
> In short, children were (and sometimes are) a social safety net.
I agree with this, and think it applies not just to children, but also to many adults, who can be helpful to their families but who might be unemployable in the larger market. The destruction of family businesses and informal employment is a problem, because society turns into, "get a job with formal compensation from one of these ten monopolies, or else you are worthless". And there are a lot of people who can't meet that standard.
For example, say your family member has mental illness that makes it hard for him to keep a job. If you owned a farm, you could still find something useful for him to do, and put up with him, and he'd be able to earn his keep, more or less.
Or say you meet a woman who, though creative and intelligent in many ways, also has unrealistic ideas about her "career", and who has never really had a proper job. So she's never going to make money, but she naturally tends to the house and does some cooking and contributes to the social life of the people around her. And say she wants to marry you. Do you do it? In a world of small family businesses, surely she'd help out somehow. In a world of FAANG-employed DINKs, she's worthless. And if she insists on living in California? "Sorry, I can't do this single-handed."
What this whole structure of society forces on people is cruelty. "Can you make money or can you not?" becomes the only important question to ask about another human being. It's horrible. At some level, Jeff Bezos' calculations of human worth enter our own calculations.
I'm not at all sure that the subjection of all things to the market has been progress. A world in which more "wealth" was in social/family networks, and where not all labor were so formal, might be a better one.