[aruanan]

However, are we to believe that by some mysterious filtering process, smoke is purified of carcinogens in the lungs of a smoker, such that the smoker exhales only safe smoke?

That may, in part, be true. However, the minuscule amount of smoke that most people encounter in environmental smoke is so small as to be statistically meaningless. Those smoking below five or ten cigarettes per day show a relative risk ratio that is no different from that of non-smokers. This doesn't mean that there cannot be an effect, but that the effect is too small to be statistically apparent. And this is for a number of cigarettes actually smoked every day. The total amount of smoke inhaled by most who encounter environmental smoke is on the level of a couple of cigarettes per year. For that matter, most studies attempting to uncover increased health risk to people who live with smokers have not found an increase in lung cancer among them (one of them that did find a slight increase was later discovered to have failed to control for "non-smoking" spouses who lied about their own smoking). Some of these studies have actually shown a reduction in relative risk, indicating a protective effect of exposure. This is not surprising since this has been found to be true of exposure to radiation as well as to other toxic substances.

[Age of Reason]

The larger picture is not whether second hand smoke is dangerous or not.

Because even if it were not dangerous (and I am not ready to concede that point)--even were it not dangerous, the opponents of smoking would still seek laws against smokers on the basis of the offensive odor of cigarette smoke, if nothing else.

The real problem here is this: The denser the population, the more a person's habits and activities will irritate others, and the more those others will turn to big government as a means to control you.