Bill Craig has some good insights on moral relativism and its problems, highlighting the important difference between moral ontology and moral epistemology, which is often confused. In his weekly Q&A broadcast titled How can People Be So Morally Obtuse?, Craig right states: “Moral ontology has to do with the objective reality of moral values and duties. Moral epistemology has to do with how we come to know moral values and duties.” Craig insists that the moral argument for the existence of God has only to do with moral ontology.
Getting at the heart of this conflation between moral ontology and moral epistemology, Craig offers:
Thus, the faulty assumption behind your question is: “If these values and duties are objective, then it seems they should have known this was wrong.” That is a non sequitur. It doesn’t follow from the objectivity of moral values and duties that they should be clearly perceived by everyone. This fact should be especially evident to anyone who has a serious doctrine of sin. The Bible explicitly teaches that fallen, sinful people are darkened in their understanding and have a debased mind and so plunge themselves into immorality (Romans 1.18-32). Indeed, Paul seems to affirm that even though people really do know that such acts are wrong, they do them anyway for selfish pleasure (Romans 1.32; cf. 2.15). The failure lies in the perceiver, not in the perceived. “The eye is the lamp of the body. So, if your eye is sound, your whole body will be full of light; but if your eye is not sound, your whole body will be full of darkness. If then the light in you is darkness, how great is the darkness!” (Matthew 6.22-3).
For the record, the argument from objective moral values states that some things are really wrong in themselves, not because society says so or because some human choices may be inherently helpful in survival while others are harmful. Abuse, rape, and child torture are really wrong and not just socially unacceptable behaviors. Conversely, honesty, love, and self-sacrifice are values that have no biological explanation and they have never been shown to help humans survive. The moral argument runs like this:
1. If objective moral values exist, then God exists.
2. Objective moral values exist.
3. Therefore, God exists.
It is important to point out that it’s not necessary to believe in God in order to live moral lives. What I’m saying is that for objective moral values to exist the best explanation is that there is a moral Lawgiver. Of course, if objective moral values do not exist, then all that we can claim that exists are personal preferences or agreed upon standards of behavior in society. For the atheist then, incest or rape may not be socially advantageous, but these acts cannot be objectively wrong, only relatively wrong. If a person can avoid the negative consequences of committing these acts, then there is nothing really wrong with them. Given enough time and change, society will alter its beliefs and moral values simply become moving targets. But the believer in God insists that these acts are really wrong and they’re wrong because God says so. But of course, this requires God’s existence. Alternatively, if God does not exist, then everything is permitted (Dostoevsky).
Either way you slice this pie, seems to me that one ends up with an inconvenient truth. Sliced it one direction, we have moral accountability before a moral Lawgiver. Sliced the other direction, and we are left with moral anarchy, which is hardly a more convenient truth.
See also the quick and keen response of Ravi Zacharias to the question “Why are you so afraid of subjective moral reasoning?”