Should marijuana be legal? Personally I dislike the very idea of it, let alone the documented after-effects. I certainly would never use it and I think that if people were fully aware of the long-term effects then no rational person would ever smoke it.
But should it really be illegal? I'm going to ignore every usual argument for legalisation; "alcohol is worse," "it will save the government money," all that. Instead, let's just ask, why illegalise it? Why illegalise anything?
I was talking with my flatmate about this earlier tonight. I said to him "if I saw you going to jump off a cliff I would try and stop you. I would try and persuade you that jumping off that cliff would be extremely painful, and if you didn't listen to reason I would try restrain you to prevent you from jumping. What I wouldn't do is punish you for jumping after you jump."
If jumping off a cliff is really that bad for you, then you really shouldn't need any more punishment on top of landing at the bottom. Likewise with marijuana. If you know fully the consequences of you using the drug, but still decide you want to try it, then why punish you further?
I'd rather have marijuana legal. If you want to smoke it, fine. Please don't smoke it near me, I don't want to breathe it in second-hand. Certainly don't smoke it around any children, as the negative effects on them are ten times what they are on you. When those kids grow up, let them decide for themselves if they want to smoke pot; don't force it on them second-hand (or worse, sell it to them).
Marijuana should be legal, but it should be restricted. People should be educated in the effects. You could say that this will be bad for society in the long run, but then that comes down to individual choice. I will choose not to use it, and so its legality won't effect me one bit. I'll be fine. If you're foolish enough to use it despite the warnings, then the consequences are on you, and there is no need for the police to chase you up about it.