Airlines can figure out how many seats per flight would be affected by fat people spilling over into the next seat, hold those seats, and then spread that cost out among the rest of the passengers through higher ticket prices. If the blocked seats are not being used by a fat person, release them to revenue standby or non-rev pax. If a pilot is assigned a deadhead next to someone taking up half of their seat, just get off, call scheduling, and tell them to try again. I agree that people should pay for the space that they occupy and that others shouldn’t be inconvenienced because someone else spills over into theirs, but that isn’t PC.