Airlines, trains, taxis, ferries and all other modes of transport charge on a
per seat cost, even though all modes of transport experience marginally greater cost as the total weight of passengers and loading increases.
"From my understanding slim people are
subsidizing people with bigger weight on the airplane traveling,...."[/quote]
Your air fare entitles you to carriage to your destination in ONE seat. You have no claim, ownership or jurisdiction over what the airline does in selling the other seats available on the flight.
A ludicrous theory to suggest you have any claim for rebate or financial consideration due to your weight or size!
Which is all fine - the bit I object to is when they take my seat as well as their own.....