If you are dressed in a suit, and you go to a baseball game or a football game, the referee or the usher doesn't come up to you and say that you are inproperly dressed and thus unwelcome. Not at all, you may feel a little out of place, but you are welcome still the same. You came to the game, you paid for your ticket, and you came to enjoy the game. Nobody really cares about what you are wearing. Casual tennis shoes and jeans are the appropriate wear, and most will be wearing them. I understand that cruiselines have dress codes, and most people abide by them, and uphold them, including myself. Anything I have to say will not change your mind on this issue, and you have said nothing that changes mine.
Last I checked, a baseball game does not specify a dress code (though there may be a presumption that one will wear clothes...). Most cruise lines, OTOH, do prescribe dress codes -- and there's an expectation that all passengers will conform. Thus, you analogy is seriously deficient.