It wouldn't really impact costs to have a row or two with 2 wide seats instead of 3 normal seats. Separating the biggest fatsos would be a courtesy to all passengers. Think about it: even if the guy bought two seats, would you want to sit next to him? He surely farts more and might not even be able to fully wipe his ass clean. I wouldn't want to be stuck for hours having to smell that. If the airline wanted to charge more, those seats proportionally should cost 1.5x instead of 2x (i.e. cheaper than buying two tickets). Of course just like how this fatso didn't purchase two tickets, he probably wouldn't have purchased the wider seat. It's kind of late to charge someone more after they've boarded the plane.