I agree. In most of my stories, the protagonist and antagonist are in a gray area when it comes to morality. I often have my antagonist doing something "evil" from the protagonist's perspective, but this "evil" act is often for a justified reason. For example, suppose the protagonist is watching tv with his girlfriend, when suddenly the antagonist smashes through the front door with a shotgun, blinded by revenge because the protagonist had accidentally killed the antagonist's child in a car crash months earlier. The protagonist has felt guilty and even suicidal for his mistake, and when the antagonist threatens to kill him, he's internally conflicted over whether he should try to save himself or let himself die. Who's the bad guy? The remorseful murderer who got no prison time or the vengeful grieving parent? If I remember correctly, it was Ben Bova who said that a story should be tellable from the antagonist's perspective as well.