I'm always wondering about how we call this planet "over-populated"... Except for freak nations like Japan or Denmark, most of the planet has vast, empty spaces. Wasteland. (Actually even Japan and Denmark have pretty big empty spaces, just not on an American scale.)
Meteors and old satellites are continually falling to earth, and nobody worries about it, because the odds of one falling in a populated places are vanishingly small. That ought to tell us something.
Food enough, they say. Well, lack of food is just due to people insisting on living in deserts. It's mismanagement. The land alone if managed right could probably sustain ten times the present global population. And if on top of the we put a few more handy inventions like the Super-Grain invented in the seventies, say, growing food from algea in the seas, then who knows.