I agree with you that people who don't drink alcohol can still cruise but I should probably not do it anymore if I for some reason couldn't drink alcohol anymore.
The reason for that is that alcohol is such a big part of the whole cruiseexperience. I love the afternoon Champagne in a lounge and wine with dinner. To spend time on the sundeck without drinking cold beer should be a real waste of time for me. And no, non-alcoholic drinks are NOT the same thing!