For the same reason that the HC bill requires healthy people, men below the age of 50, young people to pay much more than they cost - to subsidize the folks that aren't healthy, young or male. That is not fair either - but it is important so that we don't discriminate based on gender, weight, height, race, etc - everyone gets the same experience with insurance companies.

I argue that the same should be made for airlines. After all, the government has made insurance companies a quasi public utility. One could easily argue that with airfares so low today, airlines are just like bus service - a quasi utility. And as such, should be forced to not discriminate based on size of passenger, especially with it being out of the passengers control (certainly height, and in some cases, weight).