Does it really make much of a difference if it's legalized or not? I mean, if someone wants to smoke pot, they're probably going to do it. The medical excuse is a joke, again if you need it for a medical reason, you can get it. The people advocating that as a reason don't need it medically.
Here's at least one reason why I think it shouldn't be legalized, though. Think about why kids get high so much. The effect? Hmm... I don't think so. It's because it's illegal. It makes you look cooler in front of your friends. Hey, look at me, F the cops, F the law, REEFER MADNESS! It's the same as underage drinking. But the good thing about weed is that it's almost totally harmless... you're not going to overdose on it, and it won't have enough of an effect on your thinking and reflexes to do something really stupid like swerve on the road, fall off a ledge, etc.
The problem when you make weed legal however, is that the kids are still going to find their illegal fix, they still have to make themselves feel cooler. Except this time the drugs will be more dangerous. Coke, heroine, LSD, etc. That's what's happening in the Netherlands when weed was legalized. Hard drug usage went up.