Without question, this debate inspires impassioned views on both sides. Some frame it in terms of civil rights. Some argue from a health standpoint. Both sides make well-reasoned and compelling arguments, but in my opinion, they are missing the point. Pure and simple, this is an issue about physics and economics.
In any shipping business, the larger the package, the more it costs to transport. Pretty simple concept. The more something weighs, the more resources it takes to transport it from point A to point B. Fuel, energy to load and unload, and the space it requires are all tangible things that have a direct impact on costs. If you wanted to ship a car and a banjo to Europe, you certainly wouldn't expect to pay the same rate.
By the same token, if I want to fly from my home in Missouri to Los Angeles, it's absurd to think that the cost should be the same for me and my 290-pound body as it is for my twelve-year-old son and his hundred-pound frame. It takes more resources to move me to LA and I should be charged accordingly.
It matters not whether I have a glandular disorder or a Twinkie disorder. The argument that if its not your fault, you shouldn't pay extra doesn't hold water. If you're blind , you are not able to obtain a driver's license. It doesn't matter why. You could have hit yourself in the head with a hammer every day until you had no more ability to see or you could have lost your sight making a dramatic rescue of forty-three children and six puppies from a burning orphanage. The end result and its inherent restrictions are identical. No driving.
There is also a secondary factor at work here. That's the issue of basic consideration for your fellow human being. As a large man and a frequent flier, there are numerous time that I have an aisle seat and one of my fellow "Bulge Brothers" has a window seat. Invariably, there will be some small, unassuming fellow human sandwiched between us. I've always wondered how that worked. It seems to happen too frequently to be a simple twist of fate. Maybe it's the revenge of the airlines for all of the complaining and surly attitudes that seem to be the norm for air travelers these days.
We can debate endlessly about the causes of obesity, the ramifications on our healthcare system, and the contribution that fast food and marketing make to getting and keeping us big. All of those are valid subjects that deserve calm and rationed debate in their own right. However, when it comes to paying extra to move your well-marbled frame from coast-to-coast, I rely on the wisdom and logic of Newton. That's Isaac Newton, not Fig.