Actually, most people growers/smokers and opponents to marijuana alike are on the same side: keeping it illegal/illegitimate.
The growers are seeing a flooding of the market driving prices into the basement. People opposed on moralistic grounds just naturally hate it.
Smoking pot should be one of those things kept "abnormal", like gay sex. It will always exist and people should be treated with understanding and firm compassion who engage in it, but for reasons of social-learning we should never uphold aberrant behaviors as "normal"...ever...
Inhaling smoke into one's lungs is NOT NORMAL. You can call it what you like, but normal isn't something that applies to it.
It does have proven medicinal value. Therefore it should be made availible like all other prescription drugs with the FDA having total say in its manufacture and distribution. I've known people who have grown it and applied deadly pesticides to keep it looking nice "for street value" and sold it to unsuspecting ailing patients. I can only wonder how much more quickly they may have died from the toxic chemicals they were inhaling. When huge cash is involved, morality and oversight go in the trash can. There needs to be oversight. The situation is out of control.
I'm not sure what the moral ground is against marijuana.
Pragmatically, my case against it has to do with the long-term effects I've seen on people I've known. People who lost their jobs, their wives, their children, their entire lives, all because they were stuck on weed.
Most of the people I've met, who were heavily hitting the flower power, were often the most useless pathetic people. Some have told me it's great because people high on pot, are funny and humorous. Not from what I've seen. That kind of funny, is no more entertaining than kindergartners exchanging potty jokes, or tripping a drunk guy causing him to fall, or that guy in California who made homeless bums fight over $10 bucks.
It's not funny, it's sick and pathetic. And the wife who longs for a her husband to come out of his drug induced stupor, and lead her family, or the child who can't figure out why daddy never plays with them, neither finds it very amusing either.
This is what I'm against. Having met enough people in loveless marriages, because one or both, was hooked on some substance, I can say I don't want to meet anymore. And if legalizing it will increase those numbers, then I'm against it.