Once you have invented a character with three dimensions and a voice, you begin to realize that some of the things you'd like him to do to further your plot are things that such a person wouldn't, or couldn't, do.
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.
There are days when I intentionally don't write. For instance, I never write when I'm traveling, because travel is a situation where I can learn more by looking and listening than by working.
You have very accurately described the difficulty of presenting my books on film: many of my characters are alone most of the time, and when they do talk, what they say is mostly lies. That can make for a pretty confusing film.
