First and foremost, I used to work on cruise ships, but I do not think that they should be bailed out.
That said I have a problem with the points raised in the column:
1) Most major cruise companies are headquarterd in Miami or Fort Lauderdale, and they do employ large numbers of US workers. The cruise industry (not just the Crusie Lines, but also supporting organisations) generate more than 330,000 US jobs. They follow US Coastguard and CDC requirements. But their ships operate in international waters, so they are more global businesses rather than solely US companies.
2) A vast number of Fortune 500 companies are incorporated in places like Grand Cayman and Ireland for the specific purposes of avoiding tax. Cruise companies are no different from Apple, Amazon and Alphabet in this regard. That said this is the reason I do not believe they should be bailed out. If they will not contribute their actual income tax to the US, they should not be allowed to receive a US Government bailout.
3) For the individual ships they must comply with the flag state the ship is registered under. As I recall NCL did try ships registered under the US flag (they still have one: the Pride of America), but they were required to have 70% US crew and labour costs alone (especially once various unions got involved) made the project prohibitively expensive and restricted the ship to US waters. Other ships use foreign crews: there were around 50 different nationalities on the ships I worked on. International labour is cheaper. While I can't really speak for others, I was paid well. I never experienced horrible conditions, but it is a ship so space is at a premium and cabins can be rather small (especially when you've had a bad day). The ships I worked on had well funded crew welfare organisations to make sure staff were taken care of. Food and medical expenses are all taken care of. I did work long hours on occasion: the ship works 24/7 every single day, so there is always work to do. Also, you can't just pick up the phone and get more people in to help when things go wrong.
4) Cruise ships MUST comply with the environmental laws of the countries whose waters they are sailing in. Suggesting they get to hide behind corporate parents is rubbish.
Cruise ships are mostly fueled by fuel oil, which is a really dirty fuel compared to petrol and diesel. It is really high in sulfur and impurities (although EU requirements that came into effect 1 Jan 2020 force cruise ships to have much lower sulfur content in their fuels). Most modern ships have exhaust scrubbers to specifically remove SOx and NOx gasses from their exhausts. Do they "emit more sulfur dioxide than all of the passenger vehicles in Europe combined..."? While they do emit SOx, even with scrubbers, I highly doubt it is more than all passenger vehicles in the EU combined. The only source I can find for this (the OP citation is behind a paywall) is an 'in house analysis' done by the Transport & Environment NGO. A numerical extrapolation based on old data by an environmental lobby group is not the same as an actual scientific study by a independent and unbiased research organisation.
As for waste, most ships have treatment plants on board. They will hold Graywater (the term for shower and washing water), treat it until it is safe, and then release it once they are in deep water. Blackwater (the term for sewage and heavily contaminated water) is treated and held until the ship is in port when it is transferred to the local treatment plants. The only time Blackwater is released is when they are way out in open ocean (eg transatlantic crossing), and then it is only treated Blackwater that is released not raw sewage. There are trash handling facilities on board, and solid waste is held until it can be offloaded in port and is not dumped overboard.
Yes, cruise ships aren't environmentally friendly but they are not as bad as some make out. Cruise ships represent a tiny portion of the shipping industry, but are the most visible and probably the most regulated.
5) Cruise ships aren't essential, but what kind of tourism is? They do offer a way for many people to get out and travel without a lot of complication. Sure, cruise ships have their issues, but nothing out there is a perfect solution.