Secular thought likes the idea that good an evil are different sides of the same coin. There cannot be one without the other.
Some go even further by trying to claim there is a neutral state (this thought is even explored in popular roleplaying games). I've never bought this idea myself. Neutrality is essentially exclusively self-serving. History has shown that path quickly leads to evil.
So getting back to Good and Evil, I've never believed that argument that there cannot be one without the other but I haven't been able to put my thoughts together on the reason. I saw a comment on a post today at the evangelical outpost. Yes, evil is defined by good, but good is not defined by evil.
David Scott said:
It is certainly theoretically possible for everything to be good-to have a perfect life, to love and be loved by everyone... Good is not defined by evil because good is its own quality-the imitation of God and following His law, in the most distilled view.
Of course that is the Christian world view. The secularist has to reject God and therefore may be blind to the independent nature of Good. True, Evil is not being good. But Good is still good without the presence of evil.