There is a bit of a revolution brewing in airline fares. Samoa airlines is changing their fare structure to charge based on the weight of the passenger. Presumably there will be some kind of base fee + constant*(weight in kilos) but the actual structure isn't the important thing; dealing with the public relations mess is the hard part. Of course there are lots of small people and people who take minimal baggage who are cheering at the prospect of reduced fares but there will be plenty of folks who are completely against a public weigh in at the ticket counter in the airport. This does make economic sense because heavier people and luggage are actually a very big factor in airline fuel costs.
The arguments that are being tossed around over this are interesting. Note that I don't have any particular stake in this since I am of average weight and carry an average amount of luggage - it shouldn't matter much to me even if Canadian airlines start doing this. However, there are a lot of people arguing that this is discrimination because it forces people with the 'wrong' genes to pay more. There are even folks crying about sexism against men because women are on average lighter and thus pay less. Both of those claims are obviously bogus because nobody cries discrimination when large people have to pay more for larger clothes, larger cars, or stronger beds. If you are large and you want companies to do more to accommodate that you pay for it.
One argument that holds a little more merit is the issue of people requiring special equipment to move about. A walker or a wheelchair isn't optional for many people and they could be really unhappy about paying extra to have one. In the end though I still side with the airline on this: They have to pay for the fuel and the space to cart the extra gear around so charging to do so makes sense. Homebuilders don't install elevators for free, moving companies charge to move specialized furniture, and wheelchairs themselves cost money. Airlines clearly have an obligation to provide service to people with physical challenges but paying the same rate for gear isn't an unfair hardship.
I figure that this will end up something like cell phone packages - lots of different companies offering different plans. Heavy people will be incentivized to fly with flat rate carriers and light people with 'by weight' carriers and it will even out in the long run. It seems like exactly the sort of situation unregulated economics will sort out efficiently in the long run; predicting exactly how that arrangement will work is however quite beyond us.