There is not many people out there that can be classed as pure 'Evil' full stop, that is rare. Reserved for people like Hitler, Josef Fritzl, Peter Sutcliffe, Ian Brady and Myra Hindley, Fred and Rose West etc. Psychopaths and Sociopaths and serial killers.
We are all made up of shades of light and dark. We all have our defence mechanism that we are usually unaware of. And as it has been mentioned, the world is still "survival of the fittest." We are all at war with internal and external forces. Or in otherwords is it nature or nurture that drives us more. Nature is our lizard brain and unconscious drives. Our super ego is nurtured to follow rules. But Nice guys finish last they say.