Prohibition doesn't work. Enforcement is costly and never ending. Those who want to get their hands on drugs will do so whether it's legal or not. The major difference when cannabis was legalized here in Canada is that you no longer have to maintain some sketchy contact and be forced to hang out with them on occasion in order to get your hands on it. It certainly hasn't broken down society.
Most of us live in places where alcohol can be purchased legally. Well, alcohol is a drug too. Why should it be treated any differently?
What are we going to do when the state withers away? Will all sections of society continue prohibition? We should instead focus on education and providing support to those who become addicts. The idea that we can solve all drug problems by banishing drugs from society is utopian thinking.