I think a "sin tax" falls outside of a government's jurisdiction and gets into the realm of a nanny state. Antipsychotic and gabaergic drugs can produce neuro-degeneration, yet are still widely used, and the FDA has approved drugs like fenfluramine and thalidomide were used for such easily treatable illnesses as being overweight and morning sickness, yet the former caused heart-valve defects and the latter was found to be teratogenic. Tobacco treats the mood, but also has adverse effects on physical health, just like the two classes I mentioned, yet its a sin?
I don't care if you smoke three packs a day. What I care about is my living space being affected with 400 carcinogens because of your addiction. Second hand smoke kills a hell of a lot of people; restrict smoking areas so I don't have to breathe in that crap. Then we're all good.