Could there really be any such thing as horrifying wickedness [if there were no God and we just evolved]? I don’t see how. There can be such a thing only if there is a way that rational creatures are supposed to live, obliged to live….A [secular] way of looking at the world has no place for genuine moral obligation of any sort…and thus no way to say there is such a thing as genuine and appalling wickedness. Accordingly, if you think there really is such a thing as horrifying wickedness (…and not just an illusion of some sort), then you have a powerful…argument [for the reality of God].
– Alvin Plantinga
as quoted by, Tim Keller, Reason for God: Belief in an Age of Skepticism, copyright 2008, page 26-27