Er, the point of a debate is to state a claim and actually back it up with critical thinking, evidence, and reasoning. Simply saying your opinion and then refusing to explain isn't contributing anything.
It's like saying Playstation is better than Xbox and then leaving the room, or saying a game is terrible and backing that statement with "I dunno, it just is".
I don't really delve much into stuff like this, so I guess I'll keep my arguments shallow; I think it should be legalized as doing so would essentially ruin an entire form of criminal business. People using said business may be using the funds gained from it to stage other, much more severe crimes. It's a form of prevention that I predict would be very effective.
Furthermore, I know a lot of smokers myself, and as far as I can tell, they seem fine. And these guys are underage, too. But then again, I've hardly studied the effects of weed at all, so take that with a grain of salt. As trex said, this could also provide a much needed boost to our economy.