They will not use the proceeds for treatment and it will not get the gangs off the street.
Example: Tobacco payoffs to the states as well as SS fund. The advent of legal grass with taxes in Colorado has raised the price so high that it is cheaper to continue buying from the street dealer. Every one of your reasons(not new as we used to advocate the same things back in the 60’s) are all full of bull excrement. I sometimes think my grandpa had the right idea concerning drug dealers; public hanging after conviction. He said it worked pretty darn good with the train robbers and cattle rustlers.
People are mostly confused if it's good or bad. There's a really bad heroin epidemic around here. Will legalizing marijuana make those who like to be a little bit outside the law more likely to use other, still illegal drugs? Nobady really knows.
Personally, I don't support drugs, legal or illegal. I can't believe marijuana use is better than not using it. But I just don't know how to vote because it's an out-of-control situation (both the legal and illegal stuff) and nobody really has answers, just strong opinions.