In The Divine Intruder, James R. Edwards writes:

In imaginary works it is difficult to make virtuous characters as believable and attractive as bad characters. The villains of literature and screen—Captain Ahab, the boys who go bad in Lord of the Flies, Darth Vader, Norman Bates, Hannibal the Cannibal—all are, as a rule, larger figures, more gripping and more memorable, than are the heroes and heroines of even the same authors and producers. This is as true of religious literature as it is of secular literature. In Paradise Lost, Milton's Satan has all the good lines, but who remembers a word of his Christ? Dante's The Divine Comedy is one of the great masterpieces of world literature, yet literary critics as well as college freshmen rarely read The Paradiso, and those who do usually judge its virtue and bliss flat and insipid compared to the gargoyled vices of The Inferno.

There is a good reason why this is so. Human nature stands closer to evil than to good. Intrigue, scheming, and deception are more instinctual to us than love, goodness, and forgiveness. The vices are "first nature," so to speak, whereas virtue is "second nature," either a learned response or no response at all. It is easier to figure out ways to cheat the IRS than to solve the problems of hunger or violence. When we are wronged, we can hatch ten brilliant schemes of revenge; but try to devise even a paltry plan for redeeming a bad situation. Dostoevsky thus had an easier task in creating Raskolnikov, the brooding ax-killer of Crime and Punishment, than he did in creating Alyosha, the only virtuous figure in a family of miscreants in The Brothers Karamazov. This is not to diminish Raskolnikov; he is a powerful figure of darkness and depravity. It is simply to say that it is harder to make Alyosha as scintillatingly good as Raskolnikov is bad. And it is nearly impossible to conceive of a world in which the reverse would be true.