I imagine that you are incapable of reconcilining these two statements - so let me help you. There is no such a thing as fixed human nature - people's behavior is detemined by situations and interaction with others. In most situations, that interaction follows certain expected norms and rules. Which makes people look "nice." In some situations, however, the the interaction is such that it actually encourages the same otherwise "nice" people do nasty things. Jack Katz _Seductions of Crime_ provides a very good narrative illustrating that point.
So it is possible to consider people trustworthy most of time and also believe that the same people are capable of horrible things under certain circumstances. But that requires some training in social science - or perhaps treating social science as science rather than ammunitions for political propaganda.
I hope another mystery has been solved.
Wojtek