I think the devil is like god - if he didn't exist it would be necessary to invent him. If we kill the devil all we have left to demonize is each other. We need a scapegoat (ever wonder why the devil has the hind legs of a goat in many renderings?) for our baser thoughts and desires, and this metaphor is a good repository that allows us to distance ourself from our own instincts. Lust after your neighbor's wife? "It's not me - it's Satan! I swear"
