It is easy to prove. Go out and buy a case of beer and then go out and buy the same amount of Pot. In the formers case, you may have some problems yacking with your buddies over football and one may throw a can at you. In the latter, you put yourself in the position of serious bodily harm every-time you drop the soap. I think it goes without saying what causes less harm.
I seriously can't believe you posted that. That's the same exact logic the American Medical Association uses to justify their support for gun-grabbing. The whole, "if you get shot, that's pretty damn unhealthy".