Lots of interesting opinions here, out of interest does anyone know how airlines actually calculate costs/fuel usage? If they are assuming an average weight per passenger + luggage then anyone above that weight should be charged more.
Effectively, the people below the set weight limit are indeed subsidising the one's above it. It's got nothing to do with whether or not you have a choice to be that weight, it costs x per kilo to transport you so that's what you should have to pay. But, I imagine this would be offset by the additional hassle and time involved in weighing passengers at the airport. Unless your weight rarely fluctuated then you wouldn't know what you were going to have to pay for your ticket.No tickets could be bought in advance, they would all have to bought on departure, which would lose the airlines thousands in the interest they earn on pre-bookings. Not to mention the extra costs involved at the point of departure.
All in all, the seat argument seems easier to manage.