OK, so the green movement needs to get away from the words “environment,” “Earth,” and “planet,” but TV host Bill Maher has a fantastic point (for once): If you care about sustainability — hell, if you care about the future at all — you should be seriously worried about overpopulation.

Maher spoke with Countdown author Alan Weisman in an insightful, much-needed conversation. “This is a topic most environmental groups won’t touch,” Weisman began. (We will!)

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Weisman noted that Iran has the best family planning programs in history, with free birth control and premarital classes that teach just how frickin’ expensive it is to raise a kid. Plus, women are encouraged to stay in school, which delays parenthood. (As Maher says, “Education is the best contraception.”) Watch — it’s eight minutes worth seeing:

Maher also drops the sobering fact that Americans comprise 5 percent of the global population but use about 20 percent of its resources. Driving a Prius and using solar is awesome, but to really make a difference, put a jimmy hat on it.