From a lecture on God’s Existence by Boston College Prof. Peter Kreeft:
One of the facts that we observe with our interior senses is that we all have a thing called conscience. We all make moral judgments. We all judge not merely that a thing is, but that a thing ought to be or ought not to be. That’s simply a fact. Well, either moral judgments can be true or false, or they can’t. Either moral judgments are simply expressions of feelings that we mistake for judgments, or they are what they seem to be. In other words, either there really is good and evil, or it’s all an illusion. Almost nobody lives out the philosophy that it’s all an illusion, that it’s all a fantasy and a fairy tale. They may say it, they may write books about it, but when you treat them according to their own philosophy, it turns out that they don’t really believe it. All right. If there is such a thing as good and evil, explain it: why? If there is such a thing as moral obligation — if you are really obligated to do good and not evil — why? What is there behind the moral law? You see, there are facts about how things and people behave, and there are also moral facts, if this analysis is correct, about about how people ought to behave, but often don’t. What’s behind these moral facts, which we often call a moral law? Musn’t there be a will behind a moral law? We feel as if we’re being commanded, but we don’t see anybody commanding us. [...]
Where did conscience get its authority from? Where did conscience come from? Is it just one of these results of mindless evolution? The brain just happens to be wired that way? Why bow down in sheepish obedience to the accidental fact that this is how your brain happened to be wired? Why not wire it better? Or if it’s just the voice of society, as Freud thinks — if conscience is just the Superego unconsciously mirroring what other people want you to do — why bow down to them as if they’re God? And if it’s just the training your parents gave you, well, your parents aren’t infallible. But everybody, everybody — even the moral subjectivist — thinks that we ought to treat conscience as if it were God’s prophet. But if it isn’t, why should you? It can’t be God’s prophet unless there’s a God. Dostoevsky’s version of the argument is extremely simple: if God does not exist, then everything is permissible.
When I cover Nietzsche in my classes at Boston College, I try to get across his very radical challenge to my students. And one of them is, why is there truth? Why bother with truth? `Why truth, why not, rather, the lie?’ he says. And they can’t answer that. But there’s another one, about morality. Why be good, why not be evil? Why not go beyond good and evil? If there is no God, why not be evil? And nobody has ever answered that question. It’s an astonishingly simple question. Why not be bad? “Well, because we’ll catch you.” No you won’t, I’m cleverer than you are. “Well, we’ll hate you.” So what? I hate you too. I don’t care if you hate me. “Oh, because it’s not conducive to the good of society.” I know. I don’t give a damn about society. Why should I? The thoroughgoing immoralist — it’s very difficult to refute him, if there’s no God.
