From a strictly utilitarian perspective, would there be anything to be gained by, say, starting a campaign of assassination against executives of tobacco companies?

Well, it would be unlikely to convince people not to smoke. It would create a kooky outgroup faction, the Violent Anti-Smokers, that people would be afraid to be associated with, so people would become uncomfortable with being too vocally anti-smoking lest they be mistaken for one of Them. No such campaign is likely to be effective enough to make people unwilling to become the executive of a tobacco company to the point that positions aren't filled, they'd just ramp up security.

Also, deaths-caused isn't really the best metric for toll on human society. Cigarettes rarely do anyone in at thirty, while car accidents don't discriminate. Adjusting to life-years-lost would be a step in the right direction.