Exxb, all very reasonable, but why should the airline carry the extra 70Kgs, or whatever, FOC, even if there are plenty of empty seats. Every extra Kg carries a cost penalty.
The only solution is the one you suggest of conditions for obese people which MUST then be enforced at the check-in desk or gate. The critical dimension for that purpose is not actually weight, it's the width of the body, in a sitting posture, at any level (ie hip, shoulders etc must all fit in the space). It's a very easy dimension to define and check, and of course the maximum allowed is the width between the armrests (inside dimension) of the seat the passenger wishes to buy. There would be the option of buying two seats, or upgrading to a wider seat, for those who fail the test.
As a second condition, I would have no objection whatsoever to a rule which states that anyone with a BMI of > nnn must be seated where he or she will be at the back of the queue to disembark in an emergency. I can see no reason whatsoever why the lives of other people should be at risk because of the inability of the obese to move quickly, or indeed to squeeeeze themselves though the fairly ample exits. Seats for people with a BMI of >nnn should be marked as such on on-line booking charts, and a fattie who books elsewhere must be stopped at the gate, relocated to such a seat if available and refused boarding - and a refund - if not.
BMI is not a perfect measure, as we know, some very fit people have high BMI scores. But it's a start, and such people can always demonstrate their fitness to self-evacuate. (Oh Lord, here we go down another avenue....)
I always now book an aisle seat, as near an exit as possible, if I can to reduce the risk of being trapped by a tu......grossly obese person.
Last edited by Capot; 24th Nov 2012 at 14:25.