Assuming that the situation is as simple as that is foolish at best and does not adequately explain collapsing fertility rates in poorer demographics.

I agree that it would be silly to assume that the only correlation with fertility rates is GDP. There's obviously going to be many factors that affect fertility and birth rates.

There's a lot of people that assume that the birth rates will go up with income which isn't true at all. That was what my commentary was pointed at more than anything.