Reading a novel in which all characters illustrate patience, hard work, chastity, and delayed gratification could be a pretty dull experience.
I do like to explore evil characters in my books.
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.
Much of what we do in life has a huge component of luck.
But at the same time, the commonplace statement about them is true: every character is the hero of his own story. Each has a justification for his actions that is convincing to him. It's fun to give these people voices.
