Earlier quoted context omitted.
Southwest is an example of general admission applied to airline seating. By the time you're calling non-middle seats "premium", we've already lost. We should aim to have markets that provide abundance rather than focusing on extraction through things like price discrimination. It's indefensible that they sell seats which then aren't actually big enough to fit a person, whether it be their legs or their arms - this is…
There's no airline seat that can't "fit a person", that's hyperbole. Fit any person, maybe. Fit without touching the person next to you, maybe. Fit without negotiating who uses the armrest or shared spaces with a stranger, maybe. I fly frequently, I'm 6'2", I'm obese. I fit into a middle seat. Don't love it, it's not the nicest, but it's less cramped than any public transit seat and most theater seats.
I've often flown in seats where I had to spread my legs (eg into the aisle) so my knees were not pressed up against the seat in front of me. And on most flights, my shoulders are over the armrests. Talking about "the" armrest nicely demonstrates how much we've been saturated by their nonsense.
As I said, I'd have no problem if airlines charged as a linear combination of your weight and the dimensions of your seat. But rather the setup is to gouge an outsized price for a comparatively small amount of additional room, because they'll catch people at the margins over a barrel.