If two anorexic women can fit in a single seat, why should they pay for two seats?

That sounds OK as long as they both stay within the confines of that seat, share a meal between them, and their total baggage weight doesn't excede a single passenger's allowance. Unfortunately regulations require each passenger to have an individual seat belt.

If you are of average weight do you enjoy sharing half of your seat with an obese person sitting next you on a fourteen hour flight?