Pretty much I feel this is a hard issue, because of what yang says below. If someone is of a large size due to biology, they shouldnt be penalized for it. However, if you are overweight because of your lifestyle, well sorry, I dont hate you for it, but you must suffer the consequences of your actions.
To that end, I'd say that this policy walks a very fine line. People who are biologically big, very very VERY rarely come close to those who are morbidly obese size wise (Say, 300-350lb+ non muscle weight.)
Personally I say, let them charge people. If you take up two seats, you should pay for two seats. However, they must also make those seats big enough, to accomodate those whom are simply big humans (like say, shaquille O'Neal or anyone whom is generally big.) If they are able to find a good balance between making seats large enough to fit people whom are big naturally, and those whom are big because of their choices/lifestyle, I say go ahead, its fair game.
Werd. Basically exactly what I said in the above to reply to lacey
I just thought I'd be a jerk, and say that everyone has their own gravitaitonal field, regardless of size
Also, Karma is a laughable concept at best (at least karma as most people understand/use it), but thats an entirely different discussion