Actually, I think we pretty well do.
I actually think heroin would be fine, or at least not much worse than other things we do to ourselves, in moderation. The problem comes when we find that moderation is usually impossible when it comes to things like heroin. It's not heroin that's the problem--it's the abuse/overuse.
Same as murder, really. How else do we account for the death penalty? Justifiable homicide such as self-defence? War? It's not like we can go around popping people off, Dexter-style, once a month or so, but we do have provisions for how murder fits into our society. In moderation.
