In a somewhat controversial move, some US airlines have implemented a policy of charging large passengers extra. The gist of the policy is that if someone cannot fit comfortably in a normal seat, they will be required to purchase a second seat or upgrade to business class.
While some have accused the airlines of simply trying a new scheme to make money, the airlines have defended this policy by asserting that large passengers “infringe” on the comfort of other passengers and point to various complaints made by passengers about this problem.
As of now, this practice is legal in the United States. Her neighbor to the north has a different policy: Canada considers being morbidly obese to be a disability and hence large passengers are entitled to an extra seat at no extra charge.
One relevant point to consider here is what the airline is selling when it sells a ticket. If the airline is selling a single seat, then it is selling (or rather renting out) a specifically sized area. If someone exceeds that area, then they would need to buy more space. To use an analogy with time, if I rent a car for a day, but use it for two days, then I would obviously owe more for that extra day. If the analogy with time holds, then the airlines are in the right to charge more.
This point is also supported by the fact that the airlines sell their business or first class seats at a higher price than the economy class seats. Obviously, the first class passengers are getting transported to the same destination as everyone else on the flight. What they are paying extra for is more space. So, if more space costs more, then large people should have to pay more if they need the extra space.
However, if the airlines are selling passage to a destination, then charging extra for a large person would be unfair. After all, they are receiving no more than anyone else on the plane, namely a trip to the specified destination. The fact that they take up more space would not be relevant. To use an analogy, consider an all you can eat buffet. If I go to the buffet with a friend and I eat twice as much as she does, I would not be charged extra. After all, I am purchasing the right to eat all I can and not purchasing a set amount of food. Obviously, if I was paying by the item, then the more I ate, the more I should pay.
Another point to consider is the fact that being obese is considered by some to be a disability. From a moral standpoint, it is generally expected that people with disabilities should receive the same services and access without being compelled to pay more. For example, if a business imposed a fee to use the handicap ramps that allowed access to the store, then that would be regarded as outrageous. Likewise, to charge obese people more because they have the need for more space could also be seen as outrageous.
Of course, one important distinction is that being obese is generally seen as the result of decisions on part of the obese person rather than a true disability. While some people are genetically predisposed to being obese, how much a person eats and how much they exercise is a matter of choice. Since they could reduce their weight, the rest of us are under no obligation to provide special accommodations for them. This is because they could take reasonable steps to remove the need for such accommodations.
Naturally, there are those who contend that being obese is no more a matter of choice than is being unable to walk due to a congenital defect. If this is the case, then if we make accommodations for other disabilities, then we would also need to make accommodations for those who are obese. Obviously, settling this question would require extensive research in biology, physiology, psychology and philosophy. After all, it includes both scientific questions about the physiology of obesity and philosophical questions about agency and free will.