Recently, with multiple spiritual leaders and teachers, I have encountered the attitude that things of the spirit are all good and that evil isn't a factor in that world. This concerned me so I began a search as to why I'd be bothered by that attitude. How could I logically determine that evil or "darkness" existed in that realm?

We understand these things due to contrast. We know of black because we know of white, we know of high because we know of low, we know of good because we know of evil. An extreme example of this would be studying our visual perception of the world if we lived in a completely white, or black, existence. In this world all things, ourselves included, would be the same color. For our example let's assume everything is pure white. Without contrast all would be equal. Without a visual comparison there would be no difference. We couldn't even consider the color black because we would have nothing to compare it to. If that scenario would hold for the spiritual realm we could know that all was equal. In either case, though, how could we call it "good" or any other thing? Good is only good because of its contrast with bad.

From “The Quest for Spiritual Truth” by Randal S. Kinkade, copyright 2007.