If you take up two seats, you should pay for two seats. It's not a matter of discrimination. It doesn't matter why you're obese, it just matters that you are taking up more space. I sat next to a very fat man on my last flight. He was polite enough to try to hold his large arms in as much as possible, but he still took up a third of my seat with his giant belly and ass. It was so uncomfortable for me. I was literally squished. When we landed I spoke to an airline representative and said that a man of that size should have been asked to buy both seats. I demanded a 30% refund of my fare and after a long argument with several supervisors, I got it.

People here are arguing that this debate is rude, hurtful, that obese people have feelings too, that they're just "one person", etc.. But, those arguments are entirely emotional and not realistic. It's a matter of space.