My grandma and two of my great uncles died of lymphatic and lung cancers from smoking but i really dont think its a big deal. If a grouping of pixels makes you start smoking then you kinda dont deserve to not suffer the consequences.
The problem with that argument is that, due to the welfare system, EVERYONE suffers the consequences of having their tax dollars used to pay the medical bill for a totally avoidable affliction.
I suppose I should clarify. I don't mind a "fantasy" drug that is treated with due solemnity. I see so many "hur hur, wouldn't it be cool if we had moonsugar all the time like a big party hurr hurr!" threads that it seems like people want drugs in the game because they think it would be "cool." It's kind of irritating, especially when drug use (in particular, the usage that results in problematic and dangerous behavior) in some countries is a wide-spread (if not overly acknowledged or highlighted) social problem (also, think about the drug wars in other countries, where the consumption by Country A fuels gang warfare and corruption in Country B). Addictive substances tend to be destructive, and very often it seems (to me at least) that people who decide to partake don't see the negatives as outweighing the positives, which makes me think that perhaps the person is not well enough aware of the consequences.
If you want to RP an character that struggles with an addiction, or if there's a quest involving NPC with an addiction, then I think that could be a thought-provoking situation as well as a cautionary tale. In a way, vampirism and lycanthropy are similar.
The sticking point I have with realistic drugs is that people ARE stupid enough that if they might at least subconsciously make a positive association between the fiction and the reality. Or maybe even be more tolerant toward smoking in general and possibly not be as concerned about the health consequences. But, you do have a point, it does seem tenuous that the average person may have difficulty separating fiction from fact.
As for the killing argument: it was in self-defense, that suicidal bandit was trying to kill me!
Also: http://www.sciencenews.org/view/generic/id/39992/title/Gamers_crave_control_and_competence,_not_carnage.