Passive smoking should be a matter of choice and your preference
Passive smoking does not cause health deficit especially not lung cancer if it has not reached the same equivalence of proactive smoking, i.e. if someone works 8 hours in a pub 5 days a week in passive smoking conditions they acquire that in a respective quantity of proactive smoking which if added to themselves already smoking will make them have smoked more and threaten their health dependingly.
The reason why passive smoking is not affecting anyone is because it only affects the one who smokes instead of the other person who doesn't smoke and if so because they could also. Passive smoking has already been inhaled and been breathed out by somebody else than the passive smoker. Passive smoking exists as an activity and it should be a choice for those who are accustomed or who like it.