Human society consists of frail people who aspire to soemthing beyond them but fail. Some vice are unavoidably accepted as a result. The question is where to draw the circle. Alcohol is already within that circle, so with regard to it the question is of expulsion beyond the pale rather than status quo maintanace, which is what the war in drugs is trying to achive. These two tasks are widely different thus.
What you gave is a favorite among many non-example. The prescription drugs are not only within the circle by happenstance but by choice since they play a positive role. Some people will abuse them, as well as anything else, but that's another story altogether. MJ, in contrast, has no positive value other than some substitutable limit use in some cases. Legalization advocates do not suggest even that --- to make it a prescription drug. THis is a non-example.
And you will do this how, exactly, without any sense of proportionality, or any reference as to expense - either monetary or societal?
Wrong---the question really is who are you to draw that circle, and by what authority do you draw it? Seems to me a bunch of pretty enlightened folks got together in the 18th century and crafted a few documents to answer both questions, and in our zeal to engineer a "perfect" society we forgot some of the most basic lessons they tried to teach us, chief among them the notion of limited government.