Voluntary Human Extinction Movement
These guys are fun! Check out the alarmist info on thier site. Here's their intro sentance:
Phasing out the human race by voluntarily ceasing to breed will allow Earth's biosphere to return to good health. Crowded conditions and resource shortages will improve as we become less dense

And there you have it. So go see the stuff they have top say at:
http://www.vhemt.org/

Then check out the sites at:
http://conspiratorium.20m.com/pop.html