Cruising is about so many different things for different people for different reasons...I have only been on two cruises, both on carnival. I love to get prettied up in a cocktail dress for formal nights. I did not wear a long gown, but a cocktail dress is very dressy for me as I wear scrubs most of the time. My DH doesn't care to dress up regularly but on his first cruise he surprised me and wore a jacket and tie for formal night. We had so much fun.
I do however think that if someone would be so uncomfortable on a formal night just because of a jacket then take it off, I don't care what others are wearing, I am going to look nice on formal nights, so will DH, that's all that matters