Oh, I definitely agree with you that the way we're currently approaching marijuana is not working. People are still using it. Other people are still getting hurt in accidents. We do need to do something different. Personally I just think that legalizing it now, without a good system for regulation, would lead to even more accidents than we're experiencing now.
Currently, although it doesn't solve the problem, by keeping it illegal we're putting a "downward pressure" on marijuana use by sending people to jail for it. When I was young and my friends offered it to me that is one reason I didn't accept. I didn't want legal trouble. Illegalization also provides a social stigma, which is another downward pressure. I didn't want to smoke pot because I didn't want other people to think I was a bad person.
This does not work for everyone, and infact, the "downward pressure" actually appeals to some people. Some of my friends smoked weed because it isn't socially acceptable and because it was illegal. This is absolutely not the intended effect of illegalization and we do need to do something different.
But if we take that downward pressure off and legalize now without any system in place to regulate it, to punish those people who use it recklessly and keep those people who can't handle it from getting it and harming themselves and others, I forsee more accidents and more deaths than we're having now under our currently dysfunctional system.