The characters you refer to as predatory and unsavory are useful. They're the ones who make a novel into a thriller. They're active, and most of the common virtues, the signs of a good person, are not.
I do try not to spend much time reading in the suspense genre.
It's important, I think, for a writer of fiction to maintain an awareness of the pace and shape of the book as he's writing it. That is, he should be making an object, not chattering.
