It was all very very racist.

I kinda think this answers the question as to why these ideas get a pass: they offer a way to be racist and advocate racist eugenics policies without admitting you are racist, even to yourself.

I see racism in the population collapse panic too unfortunately, at least in the popular discourse around it. Overpopulation was always about too many of the “wrong” people while underpopulation is about not enough of the “right” people.