I just spent an hour+ watching The Commonwealthclubs debate on Marijuana Economics (as shown on FORA.tv). Not really time well spendt, had it not been for one point that Im shamed to say I've missed in all my years as a ganja prophet: Most illegal growing takes place either inndoors or in national forrests.
The decriminalisation of ganja would save those out of the way spots perfect for growing your illegal crop and it would drasticly cut power consumption. Growing ganja takes so much power that most growers that do get caugth; get caugth either by their enormous powerbills or they (the smarter ones) get caugth right after they get caugth stealing power.
Not to get all inn the industrial hemp debate (neutering is a sad thing wether its done to people, dogs or plants) - but another green point regarding the ganja is that it has quite unike properties when it comes to combating soil erosion and desertspread. (Thats not why you should smoke it though...)