There's so much grey to every story - nothing is so black and white.
I believe these stories exist because we sometimes need to create unreal monsters and bogies to stand in for all the things we fear in our real lives: the parent who punches instead of kissing, the auto accident that takes a loved one, the cancer we one day discover living in our own bodies. If such terrible occurrences were acts of darkness, they might actually be easier to cope with. But instead of being dark, they have their own terrible brilliance. . . and none shine so bright as the acts of cruelty we sometimes perpetrate in our own families.