When is a ‘travel hack’ unethical?

From a particular traveler point of view. Airlines are pretty few, and are consolidating, so in about 2 years you can find yourself banned from all 5-6 of them and have to take the train or drive. Has this ever happened I wonder? Can this happen? Airlines building private no-fly-lists and just refusing to do business with some people. Is that allowed legally.

Insurance companies do it:

https://www.privacyrights.org/fs/fs26-CLUE.htm

Why can't airlines? I imagine travelers who do it, would get pretty vocal online, so maybe some airline will respond publicly and say "we don't care, come to us?"...

Does the government pay airlines to fly to podunk towns that wouldn't otherwise get service, or something?

Why don't they just make that leg of the flight $50, but hand out $150 to everyone who's actually on board mid-flight? That would prevent people from booking the flight but not taking it.

Airlines are in my experience among the least ethically run businesses:

* They will cancel a flight at the last minute stranding passengers because it was "undersold".

* They will delay flights for reasons that have no accountability to consumers.

* They pass on 100% of the risk of flights being on time to consumers.

* They give gate attendants authority to claim your bag is "too large" for the overhead bin even when it fits just fine. They can even claim the overhead bins are full when they are not full.

* Airlines will try to make every seat on a plane "economy-plus" (when you have already purchased a ticket, but they haven't given you a seat assignment yet) when they are overbooked and the bump the passengers that don't pay.

On the contrary I challenge airlines to find one example where they act ethically even when their incentives are not to and the law would allow them to act otherwise.