Hmm...trust is an odd thing. I'd trust all of my players with my life, but there's one that REALLY wants to play an assassin. Even though we're playing your standard 'we are the heroes, we roll for initiative' campaign. To keep him happy, I might start an evil campaign some time, and come to think of it, this is probably one of those REAL tests.
If my players can create Evil characters who don't just kill everything, and have a motivation for being evil, then I would say I fully trust them.