I'm a smoker. I have been one for years. I can go without for a few hours. Doing so does not make me insult cabin crew, upset my fellow passengers, or a danger to the aircraft and its occupants by trying to inhibit smoke detectors and set light to paper in the waste bins.
Ayone who has a real problem with going without smoking on a long flight is perfectly aware whether or not there is a ban on board. There are legal problems with airlines handing out what could be described as drugs in the form of nicotine patches and gum, but nothing to stop people bringing their own.
Maintenance and insurance are cheaper for airlines if their flights are non-smoking, which savings are passed on to the passengers. If I was a non-smoker I would not be overjoyed to know that my ticket price is subsidising the smokers on board.
Certainly air quality on many airliners could be improved - quantity, humidification, CO2 scrubbers, etc. etc. We all know why they're not done.
For reasons of flight safety as well, I'd be overjoyed if the Duty Free system was changed to the SLF buying their allowance at destination. First, there would no longer be a litre of highly inflammable liquid per passenger directly over their heads ready to shower them in an accident (often complete with highly breakable glass containers) but also there would be fewer problems with the pax tucking in to their allowance en route and getting tiddly and repulsive.
This latter detail is one that features far more often in cases of air rage than not being permitted to smoke.
However, we know that's not going to happen either because then airlines would not be allowed to sell duty-free booze during the flight.