Not in countries like Niger, where women want 9 kids and have 7. You're saying that people intrinsically want an unsustainably low number of kids and can express that when they're free to live how they please. That people are just actualizing themselves when they have half replacement fertility. I don't think this is true, in part because I think people are more coerced by culture than you're giving it credit but even in the circumstance it were that would still have the same existential problems.

I also think you're understating the degree to which communities really did celebrate having large healthy families and held it in high esteem as a moral good. Plenty of those enclaves exist today, but they're muscled out of being represented in what Scott calls "global culture." A lot of what you're observing is just cultural hegemony from a culture that doesn't keep matriarchs.