The real problem is that most airplane seats are inappropriately sized and uncomfortable for adults of average size. I'm not particularly tall, less than 6ft., and I can't recall ever having adequate leg room on any flight except when I happen to be seated in an exit row where there is no seat in front of me. If the seats were appropriately sized for average adults, a large person (whether fat, tall, or both) would be no more uncomfortable than what an average size person is now and would not require any special accommodation from anyone in an adjacent seat.
I would not consider it any great loss if reclining was disabled in all seats. I'm not especially tall (6'), so it doesn't hurt my legs (usually) when the guy in front of me reclines, but it does destroy any possibility of using the tray table. No room for my netbook, can't put a book in there, can't really even have a glass of soda. Even when the seat is up, I'm uneasy using my netbook because the seat in front of me could recline suddenly, catch my screen, and break it.
I'm going to completely disagree, on a crowded long flight it's very hard to sleep without being able to recline the seat. The problem is that there isn't enough room between the seats.
I don't know about that, I almost always sleep on the flight sitting fully upright. It helps if the headrests do that thing where the sides can bend inward to surround your head more.
On any flight it's hard to sleep, regardless.
The seat should be half-reclined (not movable). The most important thing is that the seat should be solid. Nothing is worse than sitting on a 12 hour flight in front of a guy that kicks your seat (or sticks his feet on your armrests).