> Once they've raised the price for fatter people, why, as a business, would they lower the price for thinner people to balance it out? Why not just take more profit?
You can't assume that raising prices will cause your profit to go up. Higher prices (for heavier people) means that they are less likely to buy plane tickets, which could potentially mean less profit. So, you have to counteract this by incentivizing less heaver people to fly, by lowering the price for them, or by lowering the base ticket price slightly. Having heavier people pay more wouldn't necessarily get more money out of people, it would achieve having less weight on the plane so that fuel costs are lower.
You can't assume that raising prices will cause your profit to go up. Higher prices (for heavier people) means that they are less likely to buy plane tickets, which could potentially mean less profit. So, you have to counteract this by incentivizing less heaver people to fly, by lowering the price for them, or by lowering the base ticket price slightly. Having heavier people pay more wouldn't necessarily get more money out of people, it would achieve having less weight on the plane so that fuel costs are lower.