“The game world [of World of Warcraft] benefits from the ambiguity. What it lacks, unfortunately, is a way for players to make meaningful moral choices.” — Lydia Leong’s comment on Terra Nova, “The Horde is Evil”.
While I think that the Horde is not accurately “evil” (not moreso than the Alliance), there’s still a good point about the moral consequences of simply playing “evil” acts without taking some responsibility for what’s going on. There can be a mature gaming allowing for depiction of “evil” choices, but only within a framework that allows players to adequately separate themselves from what’s going on, and also be reflective about what’s happening. In other words, you need to play the rise of Darth Vader as the fall of a flawed hero into moral wrong, and not as a fun opportunity for griefing Alderaan.