There's quite a bit of difference between height and girth when it comes to taking up a seat though. I'm 6'5" tall with a 34-35" inseam so there aren't a whole lot of people that take up more height wise then I do, yet when I fly or go to a seated event, it is mainly me that is inconvenienced by my legs because I have to keep them in a somewhat uncomfortable manner to avoid taken up others leg room next to me. With a very obese person they are basically taking up the people's next to them space in both arms and legs. There's a pretty big difference there IMO.
I'm not uncaring, but it's just the fact of the matter, if you can't fit into one seat then you should have to buy two. Just like a parking space. If you buy a wide truck like a old Humvee, slap some wide Dana60 axles on it with some 44" x 18.5" swamper tires and then can't fit it into one parking space, then you have to feed both meters because you are taking up two spaces. Same basic idea.