"About a mile from my house is a fine old Victorian style hotel with a fine restaurant.
Shorts and casual clothes are ok for breakfast and lunch. Come dinner time, they require at least a coat."
Your analogy uses the word require, on Carnival formal attire is suggested. I think there is a big difference. I think what most people that disagree with you are saying is that they plan on dressing up (at least somewhat) for formal night but what others wear is not going to have a huge impact on their cruise. As such, it almost seems comical to see how it apparently ruins the evening for people who put so much stock into dressing up.