It’s because the very existence of veganism implies that a) eating animals and the things they produce is harmful and b) you don’t need to eat animals or the things they produce. Omnivores have to argue against one or both of those claims, or acknowledge that they’re doing something wrong, and humans will commit a lot of evils to convince ourselves that we’re not doing anything wrong
“I’m a good person, good people don’t do bad things, therefore nothing I do is bad”
Non-vegan, hearing that vegans exist: “Hey, these people are different from me! I hate them!”
It’s because the very existence of veganism implies that a) eating animals and the things they produce is harmful and b) you don’t need to eat animals or the things they produce. Omnivores have to argue against one or both of those claims, or acknowledge that they’re doing something wrong, and humans will commit a lot of evils to convince ourselves that we’re not doing anything wrong
“I’m a good person, good people don’t do bad things, therefore nothing I do is bad”
“Hey guys, check it out. I jus came up with this HILARIOUS owl-meme!”