The similarity of the effects to those of alcohol become easier to establish - objectively if not in the mind of the user. It is difficult to argue with the marijuana smoker that the brief effect is not a definite advantage. People who prefer marijuana to alcohol as a social drug resist the evidence that the two are similar, but, when grass is in short supply or too expensive, they switch to alcohol just as they use wine or beer to prolong the effect. So now we have an agent that can impair function and judgment, but the disinhibition is brief and the drug by itself has not been a problem in drivers. Organic toxicity is infinitely less than is the case with alcohol.
Excessive use is possible but has thus far been a rare problem.
My experience with Rastafarians suggests that it is difficult to accomplish even in the islands. I don't see how we can with any hope of useful outcome acknowledge that prohibition failed in the case of alcohol and at the same time apply the discredited remedy to marijuana. How can I defend the law when uniformed officers explain to me that the absence of gastritis and hangover allows them to do their job more competently than if they drank. And certainly not many people will seek treatment for the social use of weed. It would also be useful to eliminate the market that bleeds dollars into other economies, and undeniably the criminal justice system would become more useful if relieved of the burden posed by the huge number of people who do not feel guilty.