when land based Bars and restaurant that go non-smoking , weather by choice or law , the patrons still have the option to step outside to have a smoke. On a cruise no such option exists. If you ban it ship wide, until your at port guest would have to go "cold turkey", making sea day unbearable for some guests used to having multiple cigarettes a day .
I don't see this happening (banning smoking ship wide ) 15% is a small percentage of the whole but those are the ones you admit they smoke, I know some who identify as a non-smoker but will have quite a few when drinking is involved