We don't kill. People are appalled at the acts of these men. And rightly so. It is appalling. But so many people are fascinated by them at the same time.
People flock to movies about serial killers and murderers.
Look at the shelves of any video store. Who didn't want Lecter to get away at the end of Silence of the Lambs. We are fascinated with these men because they do what we do not. They go where no one else does. No moral obligations to follow society's norms.