I think it should be an option. I think some people need to calm down and let people decide. It's the responsibility of the parent, not the company, if it is rated M and there is content that concerns some.
Although I think it'd be silly if there were conversation options where the person you are talking to is like "Oh, a fellow smoker, what can I do for you?". I've never seen smokers interact that way in real life (maybe I just don't interact with smokers enough), I think it'd be silly if they suddenly show sympathy because you also smoke. There could be speech options such as "Got a light?" to start a conversation or something, but nothing that is just odd.
Trust me, as a smoker in restricted enviroment (Goverment hospital), it becomes a social thing, and you end up making connections with people you'd normally never see. And more than once I've used those smoker connections to back-door a section (what? Need a piece of equipment overhauled, bring it by. Naw, just bring it back we'll fill the forms out later). It could have definate possibilities as an 'alternate' quest completion method.
I'd also go for the whole impact on your performance (lower carry weight, running speed, healing impaired). A lower perceprion when withdrawing.
Nothing extreme but give it impact.