more than just believing that eating animal products is wrong, the disordered brain warps "right/wrong" into "clean/dirty". I witnessed this happening to myself first-hand — before I even consciously decided to go vegan, I started feeling "gross" when eating animal products.
to someone unfamiliar w/ disordered eating, this might not seem all that weird — after all, if someone has truly deeply held ethical convictions, it's only natural they would start feeling gross for betraying them, right? if someone believes animals have souls, feel pain, etc.