[pbhjpbhj]

Imagine if half of all the humans who have died didn't.

How screwed would we all be right now.

Of course it doesn't work quite like that, but still. We might save enough humans to destroy the planet faster than we can fix it ... now solve that one without doing something "evil"!

[jakobegger]

Birth control / contraceptives are pretty effective against overpopulation.

Most parents prefer having one, two or three healthy kids rather than ten and losing half of them to malaria.

[whatshisface]

The speed of "fixing" the planet scales faster than the human load on it due to economies of scale - imagine today's population with the agricultural techniques of antiquity. It would be complete global annihilation of us and everything else.