Knowing what I know, having seen what I've seen, I'd ban smoking altogether. It's a blight on society and robs women of their husbands, husband's of their wives and sons and daughters of their parents. Roy Castle is believed to have contracted lung cancer through passive smoking, caused by all the smoke-filled clubs he visited when playing trumpet with a band.
No government will ever be able to control how people treat themselves. Banning smoking wouldn't solve a darn thing - in fact, it would constrict supply, which in turn would merely mean the manufacturers would make more money. In fact, since the big factories would likely be moved offshore, it would create an entirely new black market with a huge vertical structure, with more dealers at the bottom. And that's just what we need, right? Criminals making money by giving people what they want. It's rediculous. Government cannot keep two parties from engaging in a mutually-optimal outcome. In other words, if I really want a ciggarette (either because I'm addicted or not), and someone else has them, it's to both our "benefit" if we transact. Government interference would only make that transaction more lucrative for the seller.
Case in point: since the "war on drugs," drug availability has soared to virtually every corner of the country - the price of many drugs has even lowered because of that ubiquitous supply. [And this is where I rant on a more personal level]: Demanding that the government interfere into the actions of human behaviour is absurd. We cannot expect any government to make us more responsible citizens, either by treating others with respect or ourselves with respect. Only personal values can do that - instilled from our parents, religion, education, etc.
Of course, this topic is entirely seperate from eliminating the opportunity for negative externalities in a closed, quasi-public environment (i.e. a smoke-fille restaurant). Although there are plenty of arguments on both sides of the matter, I tend to lean toward the prohibition of it within these spaces.