I sailed on a completely nonsmoking ship - Carnival's "Paradise" about 6 years ago (or about that). The last time I heard...they no longer offer that option. The ship was sold out and I was in heaven! I am highly sensitive to all types of smoke and get completely stopped up and also get migraines when around it. I can't stay in a room where a smoker has been...even after they are long gone...the cigarette smell remains and I'm immediately in trouble.
I believe the cruise lines could easily sell out a smoke free ship....as well as an all smoking ship. There are those on both sides.