I believe that evil exists. I have seen it in myself, and I think I understand the human desire to externalize it or to deny it. Denial of evil is dangerous.
From The Guardian (really): The truth about evil - Our leaders talk a great deal about vanquishing the forces of evil. But their rhetoric reveals a failure to accept that cruelty and conflict are basic human traits
One quote from this good essay:
There are some who think the very idea of evil is an obsolete relic of religion. For most secular thinkers, what has been defined as evil in the past is the expression of social ills that can in principle be remedied. But these same thinkers very often invoke evil forces to account for humankind’s failure to advance. The secularisation of the modern moral vocabulary that many believed was under way has not occurred: public discourse about good and evil continues to be rooted in religion. Yet the idea of evil that is invoked is not one that features in the central religious traditions of the west. The belief that evil can be finally overcome has more in common with the dualistic heresies of ancient and medieval times than it does with any western religious orthodoxy.