While there is definitely something to be criticized about the Christian idea of the dichotomy good versus evil, I think a case can be made that this idea has still been informative to our cultural and spiritual ideas.
Think about it: before these ideas came up, there was no real separation between the light and the dark, the animalistic and the intellectual. Sure, most expressions of this idea are a one-sided glorification of “civilized” man, but I have a feeling the dichotomy also informs our concepts of balance between two opposing forces. Without the separation and the duality of these forces, we cannot realize the value of balance, or appreciate the idea of bringing them together.
You could even say that without the separation, we cannot understand how they are related or even the same, if you are of a certain persuasion.