So what happens with people of below average intelligence and physical ability? They're likely to suffer from lower earnings. Should a person of average height and on minimum wage subsidise a well-paid tall person?
In an ideal world, chairs would adjust so that everyone is comfortable and still allow the same number of people on the plane at the same price. However, in the real world, we probably have to accept that allocating comfort based on ability to pay, with a bit of flexibility on both sides, is the best outcome.
I assume it is ok though that a short well-paid person to subsidize a tall less-paid individual?
Most airlines that I've been on have started turning the exit row into a "non-first-class extra legroom" row. On a few occasions I've seen very tall people sitting there. And there's nothing wrong with building a range of legrooms into a plane. But I don't see why there should be some requirement that a costly good - legroom on a plane - be provided to more people than actually want to pay for it.
It costs a much larger premium than the space differential, it largely costs more due to price discrimination, because many fliers in business aren't the ones paying for their tickets. If you're talking about real first class (which can carry up to a 30-50x price premium on the economy rate), there's also very attentive service, nice champagne, multi-course meals made by an onboard chef served on china plates with silverware, seclusion, sometimes even private rooms. I would not characterize it as "largely because of its larger legroom".
If you mean to say that many people choose business/first because of the additional space, that's more correct. But even in business, it's more about lying flat and other factors than simple legroom.
But a sigificant component of the cost is simply that first class carries fewer people per linear foot than does economy.
Allowing the unbundling of services is much more likely to allow the emergence of an "extra leg room only" class, than is a situation where services must be bundled into a standard package. If the prices have to be the same regardless of seat location, and be packaged with an identical bundle of food, blankets, etc, then that's a strong disincentive to attempt to sell a separate class of legroom seats. And it's much more likely that a "standardized seat" will be too short for very tall people than it will be tall enough - and even if it were, that would mean fewer seats on the plane and thus higher prices.
And it's not always as somebody pointed out above that you may chose the door seats for the same price. I had to take a last minute trip for this summer vacation. Those places were part of some "Comfort" plan I didn't even hear of while booking. Fortunately those were the only ones free on the plane and they let me sit there for free. They were booked out for the flight back though...
It's a pain, it got worse through the decades and I fail to understand that development. Was the free market not supposed to make everything better and cheaper? ;)
I'm not saying it's at all comfortable, just that it's rather hyperbolic to call it 'torture'. I have a book, an MP3 player and some headphones, and then look forward to landing. I prefer to have the money than pay for extra comfort. FWIW, I also have a pretty small car for exactly the same reason. I wouldn't call that torture, and wouldn't expect anyone to subsidise big cars just so I feel more comfortable for the same price.