I think I agree with him. Alcohol can get you into a lot of trouble. Start with DUI (serious offense most places), press on to ruining any relationships (with parents, siblings, girlfriends, boyfriends), getting into accidents, getting into petty crime and moving up to felonies, flunking out of school. For girls, drinking too much can lead to rape and pregnancy. Pot can get a kid in trouble too, but I never saw a case where pot smoking turned out worse than drinking too much. So, I agree with Obama, pot is not much worse than alcohol.
We need to remember that alcohol is very dangerous. It's legal, but it's dangerous. Pot is just as dangerous.