Is one allowed to smoke green stuff?
Sorry, couldn't resist..
Surely though, in an ideal world, shouldn't we all have a choice as to the smokiness of the social environment we wish to frequent? Few smokers actually wish to cause suffering or discomfort to anyone, and there's room in the world for smoke free pubs or rooms within. A bit of tolerance is all that is needed. As M. of H. said though, it's done now and there's no going back.