My opinion is that seatbelt extenders should [I]never[I] be alowed in exit rows; prohibiting them provides objective criteria for who is permitted to sit in an exit row. Allowing an extender forces gate agents and flight crews to decide who is 'too large' to sit in exit rows on a subjective basis.
Well that would be fine and dandy if things were uniform. However, people come in all shapes and sizes as do seat belts on these aircraft. For example, I can fit in any chair I've encountered so far with the middle arm rest down. On Southwest, I don't need an extender belt, but on many United flights, I do. So, that's like saying who is too large to sit in the exit row is up to the vagaries of what equipment you are on.
Further, in an emergency, I am the guy you want on that emergency row. Has your average passenger dealt with a door that sticks and won't open? Do they have any training working in and around airplanes. Who would be most likely to keep passengers safe after an emergency debarkation? Besides my air force friends who have combat experience, I would put my trained ramp skills up against most any passenger on that plane.
...and this is part of the problem, why is it the fat person who always has to justify himself?