Only because the fact that its illegal makes it inherent black market. Alcohol is far more addictive, but people almost never rob or kill someone for a bottle of liquor, because the trade operates in the open and is regulated and legal. Drug prohibition actually creates the crime surrounding it.
I agree but when you are talking about a drug like weed people would still grow it and sell it under market price if it was legal. I don't find anything wrong with weed but to have that many plants your kinda asking to get caught eventually.