Even the left accepts there is evil, even if they think evil is someone on the right denying people have the ability to decide what moral code they will live up to. The key to understanding evil is to understand it is not subjective. Our gut is not a device that registers how wrong something is. That is just our own response to something we think will impact us on a personal level. A comment is not evil simply because it offends us. Indeed, if evil cannot be measured, it is not evil. A value that is not measurable, has no true existence. A person cannot be good or evil if the level of their depravity does not have a quantifiable correlate. The key to understanding evil is understanding its quantifiability.
