I fully understand your logic, but I take exception to the characterization that what the cruise lines use for their tax structure is "loopholes."
And just to be clear, I just had this conversation with Anne Kalosh from Seatrade because I don't think many people (especially journalists) understand these issues better than she.
The cruise lines operate fully within the confines of Maritime law as this country has agreed to honor by treaties with the IMO. I don't see that as a "loophole." I see that as a business model based on the law of the land - just like foreign airlines flying into all of our international hubs and BP oil platforms in the Gulf of Mexico.
A "loophole" is when you have a corporation registered in the Caymans with an opaque bank account and the only listed company executives living in foreign countries ( read Windjammer Barefoot Cruising) - like a gambling web site.
On the contrary, Carnival Corp is a NY Stock Exchange listed corp with full financial disclosure. There is nothing illegal or even exceptional about what they do. They are not hiding anything, nor are the skirting any US laws.
They don't operate any cruises they are not allowed to operate legally, and they are very fully regulated by the Coast Guard, which is the U.S. representative to the IMO, when their ships come into port here. Their crews are legal employees treated with all the rights given to them by the IMO.
The fallacy in the thinking of Rockefeller and others is that because cruise ships come into US ports that they are subject to the same rules as US-flagged ships. They are not. These are foreign flagged ships working for a US corporation with foreign assets.
If you change the tax laws on holding foreign assets then you have to change them for GE, Exxon and all the other American companies that legally do business in other nations.
If Carnival ever decides to run an "American" cruise line, then they will be subject to all of the applicable laws, just like NCL-America in Hawaii, but that is not their business model.