AA should go to a fare structure where 225 pounds (total weight passenger + luggage) is covered by the base fare. Anything over pays more. Fit passengers are subsidizing fat or obese ones. I'm sure a lot of fat or obese people will claim (or at least delude themselves into thinking) they're fit, but the scale doesn't care. AA could set up new check-in lines, where you and your luggage step on a scale, an invoice pops up for the amount due and you swipe your credit or debit card. Luckily I sit in the front half the time, so my exposure to flab on the economy armrest is reduced. Circumference at stomach might be more accurate, but the number of required check-in potbelly checkers might be counter-productive.