A few points regarding the legalization of marijuana.
1) Marijuana has relatively few health consequences such as are attributed to the consumption of alcohol, nicotine, and narcotics.
2) Marijuana lacks the addictive properties of heroin, cocaine, alcohol, and nicotine.
3) We are currently imprisoning a greater proportion of our population than did the Soviet Union during its existence.
4) None of this really matters because if Obama chose to make an issue of marijuana legalization, it would isolate him politically from most of his supporters. His agenda would stall, and his political opposition would have a built-in fundraiser for the next 4 years.
5) While the social consequences of marijuana criminalization are quite severe, they are not necessarily the most pressing issues facing the current administration. It's absurd to suppose it's going to receive any kind of serious priority before the upcoming mid-term elections.
6) I also think the current situation with marijuana is hilarious. It's illegal, whether or not you believe it should be, and everyone who is currently in the criminal justice system on charges related to marijuana knew that before they chose to hold, sell, buy, or consume it. Given it lack of addictive properties, avoiding criminal charges relating to marijuana should be as easy as choosing not to smoke or sell it. If you choose to engage in criminal activity and get caught, caveat emptor.
7) He's dismissive of the feasibility of legalizing marijuana, not of the merit of its argument. He can choose to shrug off an issue of middling importance now, or he can choose to make it a major issue and toss his political capital to the wind for something that will not pass either chamber in the legislature, will not create new jobs, and will give him no leverage for pursuing his stated agenda. I'd be dismissive of it too.