The most dangerous people are those who believe that what they're doing is unequivocally good. When people set out to do good it means that they are choosing to selectively ignore facets of reality that make ascribing labels of "good" and "bad" impossible. Someone with a clear moral compass is someone who is in a "closed" state of mind; they have their perspective on the world and it makes total sense to them. A person in this state of mind will seek situations that will reinforce their value system because it feels good. And that's fine - we've all been there at some point. But, if the person has any capacity for growth whatsoever, there will come a time when these values are challenged by new circumstances and things won't seem so clear.
Good people suck. What you want are grey people - people who are confused because the world is so very complex. You want people who will question their decisions and the decisions of their peers. You don't, of course, want people who are *pathologically* confused to the extent that they cannot function, but you want people who have a certain degree of inner conflict. That is the sign of a healthy human being who is actively considering the world around them and their role in it.