Way more is being sold in stores than even estimated. I'd rather see the drugs taxed and checked for purity. It's a big health issue for drugs to be cut with other toxic fillers and concentration to be entirely unknown. 

Tax it, educate the populace on the dangers,  and fund treatment. Far better to most buyers to purchase from a safe and trusted source. And the money stays out of the cartel's hands. Cigarettes are legal - doesn't mean everyone goes out and buys them just because they can. Same with MJ and alcohol. 

Many people died when alcohol was made illegal and the alcohol was tainted with methanol, not to mention the huge rise in organized crime.