I think a fair point has been made, and one that people will rarely discuss because of the PC brigade.
Why should someone whos going to put 200kg on the plane (175kg/27st in their own wieght, and 25kg in baggage), not pay any extra for that? Its certainly gonna cost fuel! Yet someone who puts 80kg (50kg/8st and 30kg in baggage), have to then pay a fortune in excess bag charges!