The Earth is overpopulated, and also you're completely disregarding that women may not want to do the insanely hard work of growing, birthing, and raising a child in lieu of other work they find fulfilling and which could potentially have an overall greater impact on humanity. Speaking as someone who just had a baby 1 year ago - it's great and I love my little guy, but is it the most important thing I've ever done? Debatable.