You'll have to excuse me if I missed some points in the article, because I skimmed the second half. The article seems to address overpopuladion from a standpoint of population density. And, on that point, the article seems to present a valid argument against the threat of overpopulation.

But there are other issues, such as resource utilization or enviornmental impact (I'll admit, I'm having trouble thinking of others off the top of my head).