People who turn to drugs do not do it out of some disregard for the law. They do it to escape their surroundings. To assert that marijuana smoking will ruin one's life is a little off the deep end. In Amsterdam, citizens smoke pot legally, and their country is still standing. The citizens of Amsterdam have yet to sell their country for a dime bag, and I don't think they off each other for the privilege of sitting in a hash bar.
Alcohol provides many individuals with the same high, or sedation, that marijuana does.
The very arbitrary laws that make marijuana illegal deter many individuals who would otherwise smoke marijuana if not for the illicit nature of it being a crime. Anyone who has a beer is doing the same thing as someone who smokes a joint. The difference is no one fears a can of beer. Finally, we must define what a drug is. If the true nature of a social drug is to alleviate stress, or enhance a euphoric feeling, then we must certainly continue to include alcohol in the list of drugs.