I've heard people voice that perhaps the DO isn't bad--he is simply the antithesis to the Creator, and the "good" and "bad" labels are arbitrary. But once you remember that the DO rewards torturous, conniving pain-dispensers (i.e. the Forsaken) who go at any lengths to utilize atrocious man-eating trollocs to murder, pillage, rape, and steal everything in their path for personal gain--there's not much to debate.