If aircraft seats were a more realistic size we wouldn't have this problem. As for charging per kilo of personal weight, that is yet another way to screw us for money.
Have to say am disappointed at some attitudes towards larger people. I believe the average aircraft seat is around 17ins width so not surprising some 'spill over'. If the chap mentioned earlier was so huge, agree he should have booked 2 seats rather than the embarrassment of not fitting into one. Seat belts....now there's another tale. They vary so greatly that even slightly chubby people can struggle.
Have a heart folks, not everyone has a boney bum and stick-like arms