> A woman can easily have 4 children and suddenly half of the women can also be childless and still achieve a 2 children average.

The median is close to the average in kids per women in the developed world. Having four kids is harsh on many women’s bodies; eg my grandma had 8 kids, but she died in her late 50s. While no doubt some couples will want to go for four kids or more, I don’t think it’s ethical to encourage it over a more standard 2 something for most couples.