I'd like to add that alcohol was still consumed on the rest of the world, the opening of the American market was filled by legal producers and gave rise to new ones. Legalizing marijuana is just going to empower illegal drug dealers that will continue to peddle at an international level. On the other hand I disagree that legalization is a solution to the modern drug problem since drugs continue to evolve and cause mass epidemics: first it was opium, then coke, then crack and today it seems to be meth.
There is a whole culture built around the consumption of these substance that is something that won't fade by simply making it mainstream. I also think that you underestimate the level to which mj has become culturally relevant, with their own celebrities, magazines and political parties; which have garnered enough support to become a strong contender despite it's platform. A few years back it was a matter of time before this would become a strong issue and seeing as support has not subsided I will say that is only a matter of time before it becomes legal.