When the cost of an airline ticket is based strictly on the cost to move you from A to B I would say no problem. As it is now very little of ticket price is based on the costs of fuel, maintenance, ground services, equipment depreciation, pilot salary, .... Even overweight baggages charges are not based on what the added cost of a 51 pound vs 49 pound bag - it is based on what the airline can get away with charging.

That 5' 3" 105 lb, [edited] blonde is never going to go for stepping on a scale and risking someone sees she actually weights 108 pounds either.