When the adult population of a country craves something that is (potentially) bad for it then that's an education issue and a medical issue, not a criminal issue.
As the son of an alcoholic I've seen up close what alcohol can do to an individual, even so making it an illegal substance would just have jacked up the budget and risked run-ins with the law (more than there already were).
I don't smoke pot, don't drink alcohol, in general am a pretty boring person (especially when it comes to imbibing mind altering substances in company other than sweet tea) but I support those who do feel the need to do any or all of the above simply because society could not function if all these people were behind bars and every one of them has the reins of their lives firmly in their own hands. It's all about choices and mentality, making these things crimes is not helping anybody and simply drives the problems underground and creates a fertile ground for organized crime to flourish on.