most are merely undertall......
Passenger seating on aircraft isn't suited to long or wide passengers. As someone over 6ft, it's a really small space, especially when the occupant of the seat in front fully reclines. My eyesight is such that I can't see the seatback screen when that happens, even with my normal reading glasses. I have about an inch in front of my knees with my back pressed against my seat.
Having said that, it would be hell being stuck next to someone who wanted half my seat as well, it's difficult enough as it is. Fortunately most of my flying in the past five years has either been at company expense in a better seat or flying with family, and having a small child (although he does insist on getting bigger) in the middle makes it easier for the adults.