However, there is another side to this... Who are you (not you personally, but anyone) to decide how others should live their lives? If someone wants to drink soda, smoke and eat fast food, why wouldn't they? If selling what people want is somehow bad, then I guess restricting it should be good, so we should just take all these people we have decided are too stupid to know what's good for them, and regiment their life until we are satisfied? As much as I dislike and disagree with their choices, this line of thinking seems abhorrent to me, at most I'd argue we have some say on what they are doing if they use taxpayer-funded healthcare and such, but for me that is an argument against the latter, not the former. And in any case it has no bearing on the morality of the seller - he didn't ask or force anyone other than the buyer to deal with the 2nd order effects.
Viewed from that perspective, there's nothing wrong with selling cigarettes.