Population control and eugenics is the answer.
Sterilize people who insist on having more than 2 children and those who don't have the brains should not reproduce.
We start with the religious nutjobs.
'Go Forth and Multiply' type of people.
This way we reduce uncontrolled demand/consumption.
Instead of waiting for them to overpopulate before we resort to either soft or hard kill to take them out.
Better to not have these humans born than to have to kill them later to sustain the future of the entire human race.

Hi guys,

I want to recommend one documentary film which I recent watched, "Zeigeist : Addendum"
It will explain to the very root of the problem we have now with monetary based economy.
The film also proposed an alternative to the capitalism, a resource-based economy.
Watch it yourself, here is the link to the movie website:
http://www.zeitgeistmovie.com/
yes, you can watch it online FREE, just click the the picture and it will redirect you to google video. It's kind of weird in the beginning of the film but bear with it, I guarantee you that you can learn a lot from this film, and it will give a blast to your mind.