Alcohol kills more people than "harder" drugs and is much more acceptable within polite society. Same situation with tobacco, which also happens to be one of the most difficult substances to quit that we know of. Your average patient suffering from substance abuse will have an easier time quitting most drugs in comparison to nicotine. Given intravenously, nicotine is 5-10x more potent in producing a euphoric effect than cocaine.

Heroin, meth, etc. might kill you quicker and be more unpleasant to administer with more noticeable withdrawals, but if we're talking about ultimate cost to society they're not the worst offenders.