I've been looking at games like Werewolf and Space Sheep, as well as Bang!, where there are secret traitors. It's an interesting mechanic; my favourite role in Bang!, for instance, is the Renegade. The person whose identity is usually secret for the longest, and whose moral imperative is the most mysterious.
I think that were I to explore this semi-cooperative mechanic, I would want to retain the moral fuzziness of the Renegade. In Werewolf, my understanding is that we have a very classical understanding of Ontic Good and Evil. I've always liked the green-skinned races, the lonely monsters, the noble villains and the flawed heroes.
Mechanically, it would make no difference, but I think it would have an appreciable effect on player psychology if, instead of playing a "Traitor", they were playing "The Double Agent". Martin of the Fellowship of Saint Giles, in the Dresden Files, type of thing. You're not the monster in the midst; or if you are, you have a genuine reason for doing what you're doing. If you must cause pain and suffering as part of your gameplay, then you at least have a motive beyond that. I can understand werewolves who prey on a village to fill their numbers and keep their species alive. Werewolves who choose to eat people, instead of deer, because they're evil? That's fine, but it's not for me. We already have such flawed ideas of good and evil, of motive, of sin. I want a deeper discussion than that. In real life, not all cops are good (very few in my experience are), and not all assassins are bad (I refuse to disclose in a public forum my experience with assassins). I want that to be reflected in my game design, moreso than it is in the general realm of gd.