This brings up a good point.
Why should the government have any business what I do with my body? Even if a study comes out saying cannabis is actually dangerous and proves it in a peer-reviewed setting, then I'll still smoke. Why? Because I enjoy it.
Sometime along my path of education, they told me that the (utopian) purpose of a government is to protect and bring forth greater well being for the general public, which is why they're empowered to do certain things, like put restrictions on stuff they deem harmful for the public.
For instance, here it's illegal to commit suicide. I mean, what the ----? A guy who decides he doesn't want to live anymore tries to kill himself, and that's a crime? If he doesn't succeed (lives), he faces charges.
It's kind of hard to explain, but basically the reason it's illegal is because the government's supposed to protect your life no matter what. I think they said it had something to do with the superior value of life or something like that.
Anyway, just thought I'd comment on that.