> That's assuming you live alone or have no nearby friends/relatives who can watch your child.
Yes it is, because those friends and relatives also have to work in order to afford housing, healthcare, etc... grandparents that are happily retired, living off their savings and happy to donate their time is not close to a reality for many people.
> observing much poorer people having kids just fine
Define "just fine". I'm responding to the OP saying that having kids is "not expensive". It is. The fact that people make do, struggle and get by does not alter that fact, it just means they're doing it anyway. 1 in 6 children in the US lives in a food insecure home, that's not particularly "fine".
> Those societies in which few are willing to make the sacrifices necessary die out, and healthier societies take their place.
O...kay? I'm not sure a perspective that's this disconnected from personal lives is all that helpful. "Yes, raising a child in America in 2022 is difficult but don't worry, society will die and a new one will rise"... what's my reaction supposed to be there?