this, basically. The part of them that allows them to think being fat is okay is what makes them shitty in other ways. If fat were truly something that couldn't be helped, it would be different. But it can be. The fat is an outward manifestation of inner issues, and those same issues are what cause a lot of their terrible behaviour. Thin people can be assholes; I've known lots of them. But fats have their own ways of being terrible that are pretty exclusive to them.