The Fionavar Tapestry/Headscratchers

Why exactly are the Svart Alfar Exclusively Evil? I've always found it a bit awkward when fantasy fiction depicts a whole race as inherently evil, but in most cases the writer at least provides us with some explanation; in Lord of the Rings, for example, the Orcs are Exclusively Evil because Sauron made them that way. In The Fionavar Tapestry, however, there's no explanation provided. The Svar Alfar simply are evil, period. And they don't even seem to mind that Rakoth Maugrim sacrifices them by the hundreds, or thousands, to carry out his plan. Again, if Kay had provided with some explanation for this (perhaps Maugrim has direct mind control over them?), it would make more sense, but as such we have to accept that there's a whole race of inherently evil beings who obey their evil leader mindlessly, even if this means their own death.
- This troper remembers a statement in the first book about the svart alfar being 'bred to kill' and that most creatures are pleased to do as their nature dictates. It may be less that they don't care about being pawns so much as working with Rakoth Maugrim gives them the best opportunity to kill.
  - That doesn't still explain why they are so eager to sacrifice themselves for him. And if they were "bred to kill", who bred them?
  - Maugrim before his imprisonment, presumably. They are essentially his "orcs".