Although I agree with the opinion expressed, the Jones Act has nothing to do with cruising; it only affects freight carrying vessels. The Passenger Vessel Services Act (PVSA) is the law that directly concerns cruise ships that carry passengers between US ports. One of the big catches is that a passenger vessel that is not a US Flagged Ship (only one - NCL sailing in Hawaii, not including river vessels) cannot sail exclusively between US ports without stopping at a "distant" foreign port. What is a distant foreign port adds to the confusion.
It is best to quote the correct law, but it is typically not: