Good points all, and SpM brings up the important point that there needs to be amorality in Fairy tales, as Faerie is itself amoral. That's not to say
immoral, as that's quite a different thing.
Some good threads on relevant stuff:
The Trickster in LotR,
Faeries or Fairies? and finally,
Spiders.
The last one is there as inside, you will find a fair bit of evidence and argument to suggest that there is actaully one very odd and ambiguous character in Tolkien's world and that's Ungoliant.