Which in itself is a good argument to raise the standard of living from the bottom upwards .. below some ceiling of per capita consumption that exceeds current planet capacity to endure.

> Uh, poor people have way more kids:

Not in a wealthy country like the US they aren't.

https://www.statista.com/statistics/562541/birth-rate-by-pov...

Poor people get the burdens of a rich economy (ex: increasingly complex living) but have far fewer resources to offset them.

The graph you linked directly contradicts your comment.

when society rich enough, the only way can let people want more kids is offer economic help. so this is not a pure linear relationship.