You would have to take a lot of products off the market if the fact that they can make people sick or kill people were the only criterion for doing so. Yes, cigarettes are a particularly dangerous combination: habit forming, enormous long-term harm, little short-term harm, etc. On the other hand, everyone who smokes knows that smoking is bad for them -- we have had a nationwide campaign to educate people, cigarette packs must have warnings of all sorts, cigar boxes and tubes come with warnings, and we show plenty of TV ads about the danger. I suspect that banning cigarettes would do little to prevent people from smoking them; you would just see an underground cigarette trade, and attempting to crack down on it would be as destructive as the rest of the war on drugs.