I'm not an American citizen. Where I am a citizen I'm winning.
Again, do you actually have any substantive arguments against legalization? I somehow doubt it.
1. Marijuana has been shown to cause memory loss as a result of long term use. The depressant affects of it during consumption, lowering one's cognitive capabilities, are not exactly beneficial either.
2. Legalising it would be a red rag to a bull for many people, since it will lose the criminal stigma attached to it, and may well lead to its use becoming more entrenched in society in the way alcohol and tobacco are. Government's would still likely condemn it's usage, but their moral authority on the question would be nonexistent.
3. Legalising it will not magically end the problems of the illegal trade in marijuana. Dealers aren't going to throw their hands up and go 'well our work here is done'. They will find a way of undercutting the price of the legal product (which will likely have a large 'vice' tax imposed upon it).
In short, whilst there are arguments for legalising marijuana, in my view, the status quo (perhaps coupled with less of an emphasis on punishment and more of one on education) is, at this point in time, best.