And none of it requires assuming that a sapient race is just evil.
It's not an assumption. Take your pick ->
They're evil because they were created by an evil god. They're evil because they were formed from "immoral residue" that was cast off when the world was young and still changing. They're evil because they were tainted by corrupting magic. They're evil because...they're evil. Hooray for the tautology: steadfast savior of escapism.
