A lot of writers forget that evil is often pragmatic, rather than showy and doing everything for laughs. Truly well-meaning good companions shouldn't turn down actual help purely for the sake of moralizing or keeping up an image either, especially with the stakes so high as it is. It's the one thing that makes WotR's evil companions (and the cast as a whole) really stand out compared to the few unambiguously evil companions in other cRPGs, even Kingmaker.
Granted, that's not to say that displays of outright showy evil don't exist among WotR's cast. But those situations are made a lot more poignant among the sheer variety you get with the cast.
