I'd probably ban smoking, and before I get any shit for it, let me just lay it out as Pros and Cons and then arguments against each (if I can think of any).
Cons:
Violation of Freedoms (though, truthfully speaking, a large number of addictive and harmful drugs are illegal (cocaine, marijuana, LSD, etc)
Pros:
Harder for young people to be pressured into smoking because it would be so hard to acquire cigarettes.
Those who need help quitting have the struggle taken away.
Harder to get addicted (and I think we can mostly agree that there is a difference between choosing to smoke because you like it and thinking you want to because your bad habit has mentally screwed you over)
Frees up a lot of money for smokers as they no longer have to spend thousands upon thousands feeding their addiction.
Cigarette smoke smells like shit.