Alcohol is legal, sometimes is sold in state-run shops, and has controls to keep some of the capitalist stuff in check. You know, not advertising to children and stuff.
Besides, we already have the capitalist exploitation of addicts in the form of rehab.
Having alcohol illegal - or even just simply decriminalized - doesn't stop that. In fact, we were worse off since it allowed violent crime to rise instead of doing stuff like solving domestic abuse (this was one of the arguments for prohibition). Folks died since strength and purity wasn't regulated.
Which realistically hits at the point of the exchange - effects of legalisation.
Besides, we already have the capitalist exploitation of addicts in the form of rehab.