Earlier quoted context omitted.
Pointing out differences in age of first child for different groups (race, class, etc.) is not necessarily classist. It's the part that so often comes next, "therefore, we should..." that causes offense. Anyway, what's wrong with having 6 kids? People used to do it all the time and society was fine. Why shouldn't we set up our society in a way that allows this as a reasonable possibility?
Because of ecological overshoot ( https://en.wikipedia.org/wiki/Ecological_overshoot ), which is a real problem ( https://www.footprintnetwork.org/our-work/earth-overshoot-da... .). Gradual population decline through declining birth rates is the least jarring and least fascist way of getting human population down to sustainable levels.
I think this is a very important world view conflict.