You are correct - this does not make it right.
Just because the cruise lines pay lots of attorneys to draft an airtight contract, it’s called a contract of adhesion, meaning you have no say in the terms and cannot modify it in any way.
So they draft it entirely in their favor and you, the consumer, are SOL.
It puzzles me why so many on CC take the position that “The contract allows them to do it, so it’s OK.”
It’s not OK, and it’s not fair.