Smoking and drinking are two different stories, for two reasons.
First of all, one cigarette may be doing damage on its own (however slight – R’ Akiva and the rock), whereas one drink does not (if it did, there would never be a Mitzvah to drink, as there is on Pesach and Purim).
More importantly, nicotine is addictive in and of itself. One cigarette, therefore, is the first step to a lifetime of addiction. Alcohol, on the other hand, is not addictive. Sure, there are alcoholics, but their addiction is to the effects that the alcohol has on their emotional states of mind. One who is emotionally healthy will not become an alcoholic.