By definition, a human being is endowed with free will. He can use this to choose between good and evil. If he can only perform good or only perform evil, then he is a clockwork orange - meaning that he has the appearance of an organism lovely with colour and juice but is in fact only a clockwork toy to be wound up by God or the Devil or (since this is increasingly replacing both) the Almighty State. It is as inhuman to be totally good as it is to be totally evil. The important thing is moral choice. Evil has to exist along with good in order that moral choice may operate. Life is sustained by the grinding opposition of moral entities. This is what the television news is all about. Unfortunately there is so much original sin in us all that we find evil rather attractive. To devastate is easier and more spectacular than to create.
