As free-thinking humans, do we not feel inherently guilty of the lack of fulfillment of the responsibilty this thinking gives us? Do we not believe ourselves to be the failing gardners of this eden, our world? Are we not alone in pitying the poor beasts we must slaughter to feed our hungry children?
And then we are presented with an excuse, a get-out clause, a redemption.
"It is not us that has failed, but it us that has been failed! For we have been subjected to a greater force, an unbending will that turns the weak from their role and sullies the work of the kind and noble. This will has a name and that name is Evil and all who presume to do good should fear it, for it will tempt you from the path of good, the path of God!"
And so now it is all very simple. We are but pawns, it couldn't possibly be our fault. Christianity has capitalised on this. The fanatic general, the ruthless CEO, the lying politician, all are saved as long as they give themselves to the cause and ask for forgiveness.
My point is not to deride the church or any other similar religion, but to demonstrate the state of mind our species endures. Not only is guilt a product of our free-thinking but a treasured assurance of such thought, and religion provides the ultimate crutch. Now presented with an encompassing unknown, such a mindset will try to align the experience with it's own education and recognise the unknown as either Good or Evil. Consider what would happen if you sent a photo/holographic picture of somebody back a 1000 years. The main reaction would probably be fear of the 'devil' or 'spirit' in the paper, even though we know it wouldn't harm anyone their fear of the unknown wouldn't offer such comfort. In fact consider the initial beliefs on the invention of the camera, that such a device captured the soul.
It may well be that Evil exists in the observable form, but who is to say that the entity/experience labelled Evil and the religious construct of Evil are the same thing.
Fear, guilt and faith are blunt instruments in the dissection of Evil, science and understanding are the tools for the job, and although it may take a long time and the conclusion may be the same, the answer will be greater to our satisfaction.
PS sorry about the long post, got a bit carried away there!