I highly recommend a book by a genuine epidemiologist at Einstein College of Medicine. It’s called “Hyping Health Risks”, by Geoffrey Kabat, published by Columbia University Press. He shows that the incidence of lung cancer among non-smokers is so small that almost any attempt to find causality is doomed. In particular, second-hand smoke is so vastly diluted compared to what’s inhaled by a smoker, that no ill effects are ever likely to be demonstrated. Rather, the idea of second-hand smoke was seized on as a way to keep anyone from smoking in the presence of other people.
Smoking is indeed dangerous, and every legitimate effort by poskim or, l’havdil, the government should be applauded. It’s interesting that another demonstrated health risk is given a complete pass. Mishkav zachor is much more dangerous than smoking cigarettes, but the Supreme Court has ruled it muttar.