Right?! I used to think a lot about that kind stuff a lot and I have theory about it: They see a vegan simply existing and (maybe subconsciously) think "shit, not eating meat etc kind of makes sense" but then instead of learning from it, they take it as a personal insult almost. Like "fuck you, you're not a better person than me". Then the initial reaction is to deny and deflect and throw shit, so you can delegitimise the argument and won't have to think about it critically. Same reason that people who like to drive cars a lot might dislike cyclists, or why some people are instinctively annoyed with people who are athletic. And now that I think about it, the same thing happens when libs face criticism from the left. Probably this is already a really basic psychological concept that I re-invented, but anyway.

They can't be doing the wrong thing. They're the main character.