Quoth Hans Rosling: "child survival is the new green."
The idea is that once folks learn that their kids will make it, they quit having 6 of them just to be sure. Therefore lower population growth.
Either that or the kinds of societies that have their shit together well enough to distribute condoms and the pill reliably also happen to be capable of providing offspring with a healthy environment and medical care.
Either way, Bill Gates's fight against malaria seems well justified from a long-term perspective.
The fact that kids aren't dying of a terrible disease in the short term is probably a decent thing too. That way they can grow up to buy Windows7 phones.