All the moral issues aside I think there is one big reason that will prevent mj from being legalize anytime soon: too hard to regulate it. So many already grow plants in their backyards and will continue to do so even if it is legalize so they can get around having to pay tons of cash for it. I'm sure it would put a big dent in the drug dealers trade but there would still be pot sold illegally. "Tax the hell out of it" a lot of people have said would only result in people doing what they do now: buying mj illegally.
Another issue I see is duim? Driving under the influence of marijuana? As far as I know there is no way to test for mj content like a breathalyzer can do for alcohol. I may be wrong on this but I don't read up on this crap all the time, my drug days are eons behind me. If they use a blood test or urinalysis 1) EXTREMELY expensive and 2) Inconclusive due to the length of time mj stays in the system. So, how can the police REALLY tell if someone has smoked too much and gotten behind the wheel? How do they set a "legal limit"? They can't.
I think the above issues are much more pertinent to the legalization of mj than all the moral stuff that has been previously brought up. Right or wrong, mj is becoming socially acceptable and even "cool" (as stupid as that is) in a lot of circles.
And for people who's best defense on EITHER side of the issue is quoting bumper stickers from the 60's and 70's. (i.e. support your local farmer?) All I can say is...get a friggin clue!