People have spend decades in prison for selling weed. Now it's legalized in more and more countries. Making things people like illegal rarely works, and it's far from a "solvable problem". Don't get me wrong, gambling is very bad, but if we were to analyze it statistically I think alcohol is way worse for society at large. And we all know how making alcohol illegal went.
Legal weed has been a disaster in the US, 20 million addicted (almost daily use/daily use) versus a few million before it was banned.