I don't think interfering with someone's business model is inherently unethical. While intentionally booking a flight this way deprives the airline of some oppo

I don't think interfering with someone's business model is inherently unethical. While intentionally booking a flight this way deprives the airline of some opportunities to make money, not boarding the next flight doesn't deprive them of anything. In fact, it saves them a bit on fuel and may even open up a seat on an overbooked flight, saving the airline from paying compensation that usually exceeds the ticket price. What actually seems unethical to me is that airlines have contract terms forbidding getting off early. An honest and effective, though not profitable means of preventing passengers from doing so would be to charge less for one leg than for two.