People are fascinated by evil because it's mysterious and it doesn't seem to have a rationale behind it, and the second you say that Hannibal Lector was abducted as a child and he had to eat his sister or something like that, it becomes immediately mundane. The character becomes mundane.
“Kind thoughts are rarer than either kind words or deeds. They imply a great deal of thinking about others. This in itself is rare. But they also imply a great deal of thinking about others without the thoughts being criticisms. This is rarer still.”