To become addicted to something (willingly) is sinful.
There are serious health problems with cigarettes. Just because not everyone experiences them, doesn’t mean they aren’t there. I’m not saying it’s necessarily a mortal sin, but it’s definitely a venial sin to smoke cigarettes to excess (as it would be with cigars or pipes). Anything done to excess is a sin.
On a cultural level, cigarettes are pretty disgusting and are quite off-putting to most people. They have so many chemicals in them (and, I’m pretty sure, a lot of added nicotine to induce addiction), that I can’t see how one can say that the proportional benefit of them is sufficient to subject one’s body to these negative effects, especially when there are so many other forms of tobacco use that have no serious long-term effects on health when used in moderation. That being said, I’m not going to say that someone who smokes cigarettes in moderation is committing a sin. I just think it’s low-class and pretty disgusting. That being said, I regularly smoke cigars, occasionally smoke a pipe, and use nasal snuff frequently.