If that's the case, then a comparison to Prohibition is not fair.
Imagine if during Prohibition we legalized just beer. Or wine. Would that have had any affect on organized crime?
In your scenario, we'll end up with legal marijuana (and all the ills that will come with that), and we'll still have the criminals dealing whatever remains illegal.
Marijuana only accounts for about 20% of what Americans spend on illegal recreational drugs. Legalizing cocaine and methamphetamine would have a much bigger impact on the criminals.
If that were the goal.
I was basically comparing pot to alcohol and not to other street drugs. In my opinion the social costs and the criminal behavior that are a direct result of cocaine and meth use justify those substances being illegal. We as a society have a legitimate concern with substances which are known to cause criminal behavior or which put a disproportianate burden on society. And yes I know alcohol meets those criteria in some instances- which is why it is regulated. But that applies to a minority of users. I believe the same of pot smokers. But coke( especially in base form) and meth are just way too dangerous to allow their legalization.