It is easy to pick out the good dwarves from the villains in Guild Wars: they have faces and quite often names. The Stone Summit dwarves are faceless and nameless and therefore it is okay to slaughter them in groups, while you are supposed to care about the Deldrimor dwarves with names and faces. Also, it is almost always okay to kill the red dots, while the green dots are your friends. Morality is baked into the UI.
See also the Cracked Star Wars explanation for why evil empires want closed-face helms but how that potentially hurts them when everyone turns out to be more empathic than previously suspected.