I don't buy the over population arguments. I think they are well intentioned, but misguided in their goals.
The high population is due to the stagnation of the people. Rather than looking after their own interestes, defending farm land and a reliance on comfort building technology, people live long on diets of drugs that sustain their meaningless lives, and then they breed and pass on a culture of stagnation.
The threat to the world is not the population (they could all fit in Texas comfortably), but rather the wasteful activities of that stagnent nation and the demands they put on business. Stop supporting losers (broken record) and the population will either live within their means or perish in their inability to provide for themselves.
The ones who live will be fewer in number, but the quality of their character will be higher.