As the New York Times reports, both Southwest (LUV) and Delta (DAL) have recently made it more difficult or expensive for flyers to snag a coveted window or aisle berth, and American (AAL) and United (UAL) are expected to implement super-discount fares, probably with similar restrictions, soon.

Get Data Sheet, Fortune’s technology newsletter.

From a business perspective, it’s an obvious move—because the middle seat, as any frequent flyer can attest, is a waking nightmare. Literally, waking, since there’s nothing to lean against for a nap. A trip to the bathroom inevitably involves awkwardness. Getting at your carry-on is a feat worthy of a circus contortionist. And while common decency would seem to dictate that the middle-seater gets both armrests, my unscientific personal research suggests no such idea has taken hold in our dog-eat-dog world.

That’s also why this shift may get even bigger public pushback than other aspects of “unbundling” in ticket pricing. Getting a better economy seat has for years been about being first to book or check in—a kind of meritocracy. And as much as we groused about baggage fees, economy flyers have all had to pay them together.

For more on airlines, watch our video:

But making the middle seat a ‘discount’ option—a nice way of characterizing a surcharge on window and aisle seats—threatens to fracture that community of co-sufferers by creating a third class of passengers, right next to everyone else. A poke in the ribs is tolerable when you’ve got nothing but your own lack of foresight to blame. But knowing that the passenger next to you gets to spend the flight staring at the sunlight glittering on the ocean, just because they had a few extra bucks to spend?

That’s the unkindest nudge of all.