I think this topic is taboo, since most players are of such a young age. However, I'll still put in my two cents.
There is nothing wrong with Marijuana, as a plant. I think your argument about abuse is wrong. Anyone can abuse and get addicted to anything, given the right circumstances. Even I had a relationship with marijuana. The social circumstances I found myself in were negative. For me, my addictive "use" was based on escaping reality. My grades slipped, I started staying up past 3am reasons of the culture, and just didn't care about anything. Especially the things that mattered.
Now, after saying that, I must say that prohibition is wrong. I believe that the government chooses to keep it illegal because it is easy to grow. You don't see people growing tobacco in their houses. They cannot tax what isn't being sold. So, if it was legalized, you would have a federal profit and strong army of underground growers that would "abuse" the terms of the law. Even if the government sells plants with no seeds, plants still exist out there under all of our noses.
Now, the positive arguments are good, but I think the majority of people would simply abuse marijuana for the sake of ability. For at least a few years. It still destroys brain cells, has similar tar effects to smoking cigarettes, and will be abused. However, people have a right to choose what natural substances they want to use. And I agree, alcohol is ten times worse than marijuana. But that doesn't mean that marijuana should be welcomed with open arms. It's still detrimental to the young and immature of our society.