[Amahain]

Yes, I'm aware of their death animations. I'd say it's open to interpretation. Maybe it's their uncorrupted soul escaping their bodies. Maybe it's the demonic spirit that possessed them that's escaping their bodies. The game never makes that point particularly clear, and establishing canon based on a death animation seems a bit shaky to me.

And I'm still not sure if I really understand the complaint, here. There's plenty of precedent in the Diablo universe for demons turning mortals into demonic looking creatures. Succubi, corrupted rogues, goatmen, and council members were all humans once. If my mistake is labeling these corrupted people as demons, then it's a mistake that people on the Diablo team have made as well. Succubi and goatmen are specifically referred to as demons in the manual, and all four monster classes are demons according to the game mechanics.

Anyway, it seems like a minor quibble to me. Diablo lore isn't entirely consistent with itself, never mind my interpretation of it.