Here's my letter in response.
You fell for it.
Airlines build their planes with seats and seat pitch that are uncomfortably small for most people, because they want to squeeze more people onto the plane and increase their profits. They rely on the prevalent fat hatred in this country to deflect blame onto fat people.
Americans have grown larger in all dimensions - taller on average than 30 years ago, as well as bigger around. And in the same time, airlines have decreased the width of their seats and the space between seats.
You point out that 2/3 of the people in the US qualify as, to use airline terminology, "customers of size."
I ask you, does it make sense that an entire industry should build accommodations that fit only 1/3 of their customers, and decrease the size of its accommodations while its customers are increasing in size?
I suppose it does make sense if the industry has apologists like you who are ready to put the blame for your discomfort in airplanes somewhere other than where it belongs.
Guess what. Fat people hate sitting in a too-small seat next to a fat-hating person just as much as you dislike sitting next to them. They hate touching you, feeling your body heat, and smelling what you ate just as much as you hate it.
A word of advice. The next time you find yourself seated next to someone you deem too large, be brave and risk their feeling insulted. Go ahead and ask to be re-seated, rather than waiting until you get home and safely doing your insulting in a newspaper column instead. You'll do everyone a favor.
ETA: The Denver Post phoned and asked if they could publish my letter.