I think pot (and maybe harder drugs) should be legalized because I don't think we should stop people from ruining their own lives if they want to. That being said, the Mafia wasn't neutered with the end of Alcohol prohibition. The cartels will still be in control if we end drug prohibition.
There still an "issue" with moonshine in places. (I think only people that really have an issue with it are legal distillers, but I digress.) That's not the point. The point is that all of the organized crime that was empowered by Prohibition didn't go away after the end of it, and in cases got worse.
Well it would free up billions and billions for rehab. It is very difficult for poor folks to actually find decent rehab facilities. Of course given conservative hatred of government unless for prisons or wars, it is not all that clear that merely defunding much of the prison/"drug war" expenditures would be spent on drug rehab. Prayer and appeals to personal responsibility would probably be the only suggested solution. Without their profits to spend on gunmen and bribes it would be fairly easy to round up the ex-cartel leaders. Could it be that the Latin Americans could actually win the "drug war"? Let us hope so.
The mafia was neutered when it came to alcohol, they just branched out into other illegal enterprises. If we regulated drug sales and use, the people who are currently in the cartels may have some control over the manufacture and distribution of drugs simply because they have the expertise, but they will be following the rule of law, subject to regulatory scrutiny, and taxed. That would be infinitely better than the situation we have today.
I have never heard of a single instance where the mafia got worse after prohibition. Do you have anything to substantiate?