It's not inappropriate for discussion, it's just wrong. People who are rich and healthy don't have kids above replacement rates. We don't know why but we've observed the effect within countries, between countries, and across a broad range of cultural and religious groups. Economic improvement and public health aren't in opposition to population control measures, they are population control measures.

The correlation doesn't seem to hold at the high end, and much of the data in the western world confounds population growth due to fertility (still low) with population growth due to immigration (which has upticked across the board in recent years). As far as I know, though, the effect is still strong in the delta range that the Gates foundation is targeting.