"In the grand scheme of things overpopulation isn't that big of a problem"
Depends if you want to be wealthy. Overpopulation limits the wealth potential of the people that live there. China having less people than India is a good thing.
A collapsing population is a bad thing. A stable not growing one for a large population country is good.
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The problem in Asia is the youth population 0-5 years old is almost half the 40-45. A stable population would now require 4 kids per family to avert losing half the population. That is not good.