Sympathy for the Devil

In his Poetics, Aristotle proposed that we typically do not sympathize or empathize with a completely blameless character nor with a reckless villain devoid of all virtues. However, do narrative art forms indeed preferably portray characters who occupy the middle ground between these extremes? Is there not actually a bias in favor of dark characters?
Clearly, morally blameless characters and lives have barely ever been at the center of novels. Diabolic characters, by contrast, and great criminals have powerfully captured the mind of readers. If so, how does this relate to recent revivals of classical claims that literature is a school of empathy and, by implication, makes us more sociable? Our study will investigate the attraction of criminal and diabolic characters against the background of the empathy hype in current studies on reading literature.