Perhaps the reason that “corpse” seems such an odd way to term a dead animal is that “corpse” is normally reserved for dead human bodies. Dead animal bodies are generally referred to as “carcasses”, not “corpses”. Using the term “corpse” is a rhetorical strategy for blurring the distinction between animals and humans.
I agree that there are some people (I’ve met them) who seem genuinely unable to hold in mind the fact that pork comes from a dead animal while they’re eating a ham sandwich. That IS silly; I mean, how disconnected can you get?
But you have to remember, when vegans refer to meat-eaters as “corpse-munchers”, or whatever the “au courant” term is, they’re not just trying to educate people on the fact that they’re eating dead animals; they’re going beyond that and implying that they SHOULDN’T be. The term is intentionally accusatory. I wouldn’t say that the reaction of (most) people to vegans is so much “frightened”, as rather somewhere between amused and irritated.