Oh it's certainly their right to set the prices, but I wouldn't automatically say it's their right to dictate which tickets you use post-purchase.
I wonder what I would do if I were the airline. Obviously the simplest thing would be to suspend the return ticket, but I suppose that the return ticket would typically be booked on a different airline. Another option would be to collaborate with other airlines to suspend return tickets, but I suppose that would be collusion and wouldn't fly with regulators. You could also try a prisoner's dilemma-y thing where future sales to a customer that has hidden city-routed in the past are marked up to fix the difference. If all airlines did this then only infrequent flyers would be able to hidden-city route. But if any airline refuses to participate, it might be tough for the business of the airlines that engaged in this practice.
Tough situation for the airlines. Not that I have too much sympathy, but I do take it into perspective that travelling is historically extremely cheap. It's a great time to be a flyer.
Comparatively, the duties and rights regarding a physical good like a sandwich are fairly simple -- it behaves like most simple physical goods. You buy it, then you can do what you want with it. Airline tickets are unlike this in a variety of ways. Hidden city routing being prohibited would not, I feel, be qualitatively different than many of these other restrictions.
I buy airplane seats; I can sit in both seats or just one. If they don't like which seats I chose to sit in or not, they shouldn't have sold the ticket to me in the first place.
I think the airlines would be willing to ignore a handful of people skipping out on a leg here or there. Pricing is obviously a major issue, but I think even moreso than that, if this were to become a common/well accepted way of buying tickets, there are serious issues in case of cancellations/delays/missed connections that, while fine in the hands of those who know they're subjecting themselves to the risk of being stranded, would lead to a bunch of "I bought a ticket to Chicago and United is going to leave me in Nantucket unless I buy a second ticket" news stories in case of a snowstorm.
They really are.
Coca-cola are marketing a refreshing tasty sparkling beverage, but what they're actually selling is carbonated water with sugar and acid. If I use it to clean my driveway, that's my prerogative, and Coca-cola don't get to retroactively charge me more because driveway cleaning chemicals are a more profitable market.
The government wanted to tax people it they drink it but not if they just clean with it. But then people (well, alcoholics mainly) realized they could buy the untaxed one "for cleaning" but then turn around and drink it. Can't have that!
End result: denatured alcohol, which (given taxes) is cheaper than the drinking kind because they "yuck it up" to the point that you can't drink it.
I just hope they don't do the analogous thing here, which would be like "poison you and hold the antidote at the ticket's final location" :-O
The statement you made about airline tickets is normative, not descriptive. I'm curious about how things actually are, not how people on HN want them to be.
http://www.aa.com/i18n/customerService/customerCommitment/co...
As you can see, hidden city routing is prohibited, and they retain the right to assess the difference between the ticket you actually used and what you paid if you engage in the practice.