Of course, the definition of evil in this case isn't quite written in stone -- what your character thinks is OK to do may not be what you think is OK to do. My undead Rogue took a lot of pleasure in killing Stanley, even if I would be horrified to hear about someone doing the same thing in real life. But in the same vein, while I was fully convinced in character that setting off that Mana Bomb in Outland was the right thing for my character to do, personally, I thought the kill count was a little shocking. At what point does my hero become a mass murderer?
A few other WoW Insider writers mentioned the Cenarius' Legacy and the other Undead Plague quests to be a little too evil for their tastes. Are there any other quests in the game where your character is asked to do something morally questionable?