Marijuana has been a medicine for thousands of years more than it's been an illegal herb in a nation dominated by persons so pathetically retarded as to be a waste of breath.
In fact, study after study shows that marijuana actually defends against cancers - where as the legal tobacco is full of carcinogens and is legal.
It's a perfect testimony to capitalism and mind control via mass media - the populace is so stupid that I can hardly comment on it.
Why is it illegal? - human ignorance, and the power of corporations to control stupidity.