I like your 2020 vision. You can see right into the future. But we want it not illegal now, in fact 40 years ago even.
I don't even smoke it and I wish they would legalize it. We waste so much money, space and time prosecuting weed offenses. I really don't think it would increase usage either. In all the time I have considered smoking it the law was never really a factor. I guess since legal trade and growth would drop the price that could help, but the price of enough to get high isn't so extravagant as to be a big deterrent either, and if the goal were to keep the price high doing it by making people have to fight drug wars to supply it is a pretty stupid way. I say legalize it and tax it. Let the profit go to better schools which reduce crime instead of gangs that cause it and cost the public money in law enforcement and prison.
within 5 years of universal legalization, everyone looses interest and could care less. (other then a few diehards still trying to make some kind of religion out of it anyway)