For us, formal night's gives us a reason to dress up. Depending on the coast you live on, and we live on the west coast, most people dress from casual to sloppy, cruise or no cruise. Business attire seems is limited to upper cooporate levels. So we look forward to the opportunity to wear 'dress up' wear.
The only caveat to this has been in 'air travel'...packing suits, gowns etc. With the suitcase weight and size guidelines, we intend to travel lighter and with way fewer pieces of luggage. My husband will rent a tux and I will bring only wrinkle resistant, light weight type evening dresses. I've seen some that are simply lovely and pack easily. Yes, it's a challenge and it can be done...but it does take planning.
I do agree, if you don't want to dress up on formal night...it's no big deal...simply eat at one of the alterative restaurants. Don't take a 'juvenile' stand on the issue. Save your protests and bravado for something that has real meaning. Walking into a restaurant in your shorts and T'shirt, when everyone else is in formal attire is making a statement about yourself and standards, just not the kind you think.