I was not talking about devils or morality or anything like that. I was talking about whether all undead are inherently evil necessarily just because they are undead. Indeed, per the 5E Monster Manual, page 147 under the entry for Ghost it says, "Ghost. Medium undead, any alignment." I have never before seen a good ghost in a D&D module, but I guess if it fits the story, then I'd be OK with it. There sure were a lot of them at Hogwarts.