If we wish to build true peace, how can we separate, or even set at odds, the protection of the environment and the protection of human life, including the life of the unborn? It is in man's respect for himself that his sense of responsibility for creation is shown...
Furthermore, as I noted during the recent FAO World Summit on Food Security, 'the world has enough food for all its inhabitants' provided that selfishness does not lead some to hoard the goods which are intended for all.~Pope Benedict XVI, making it clear that abortion is not an acceptable means of protecting the environment, as quoted by Zenit, January 11.
Taking a functionalist view of humanity is typical of people who argue for abortion. Overpopulation is no argument for murder. Society is a way of structuring civilization, created by humans, for humans. It is a tool intended for our benefit, not the other way around. If society is broken -- in other words, if some people have plenty of space, food, and other necessities, while others have too little to survive -- we should no more consider killing people than we would consider cutting off our feet if our pants didn't fit.
Overpopulation is a myth perpetuated in the West by people who would rather advocate killing "extraneous" humans than give up their Xbox 360 to feed a hungry child.