Let's just say 'eating people is bad' and skip the pointless semantic argument that sounds like someone trying to excuse eating non-human sapient?
Yeah, that's pretty much my position as well.
The reason "eating fellow humans" is morally Not Okay is not because it's "a creature eating its own kind." It's because you're eating another sapient being. Thus, the morally relevant thing is "eating another sapient being." It sure would be nice if we had a shorter, more pithy term for that, but because non-human sapient beings are more rare than people who have no strong opinions about any grammar topic whatsoever, we'll just have to keep using the clunky circumlocution "eating another sapient being."
And yeah. Vampires, illithids, etc.? Fine calling them "always evil," along lines like my last post. My illithids (rather, singular, since only one has ever appeared) COULD eat other things than fresh, sapient brains. But any who choose to do that ARE evil, and that evil really does leave a mark on the soul. (They even have cloning tech, so they COULD just reproduce with clones...but they don't, demonstrating their evil.) Maybe eating sapient brains even stains an illithid's skin dark purple-green, so you can even dodge the "but how do you KNOW they're evil" thing.
I use these things sparingly. The one illithid was quite evil. (And his hubris killed him, delightful irony.) Devils? They're scary, but not because they're violent. It's because they're manipulative. They don't tell lies or try to
trap people in bad deals--because that's stupid and bad for business. They'll give you contracts that only ask you to step just a little outside your moral bounds, to do something you think is good. And every step they persuade you to take down that road makes you more and more like them. Even if you decide to opt out, they've made the world more like them--which is a win for them.
Pure evil is a nice palate cleanser; that and non-moral conflicts (e.g. actual animals, non-lethal competition, etc.) They help highlight and sweeten the complex conflicts, difficult moral choices, and deep character reveals. It's a refreshing gulp of water or bit of citrus juice to cut through the richness. You wouldn't, in general, want exclusively that palate-cleansing and nothing else, unless you were getting your fill of those other things elsewhere (which is fine! but not super relevant for me). But such things serve a useful purpose, when used sparingly, so things don't become too ponderous or over-saturated.