It's because too many people abuse it like they do alcohol It might be harmless in itself but when all these idiots get hold of it they just act like dickheads. Plus, it can have psychological effects, I've known guys to do it where they've gone off and they start rocking saying they want to be alone, having a bad turn an shit. People abuse the shit out of alcohol, you don't want a bunch of these mongs running around pissed up and stoned, who knows the stupid shit they'll do