Atheist Kai Nielsen argues that it doesn’t take God’s existence for us to figure out what is just and fair in a given situation. Do we really need God in order to know that we ought to keep our promises, or tell the truth, or pay our debts, or allow an elderly woman to take our seat on the bus? If we want to be treated with respect and dignity, isn’t it only reasonable that we should treat others with respect and dignity? It doesn’t take the existence of God for us to figure out how we ought to conduct ourselves morally.
Both Kai Nielsen and Immanuel Kant are right when they suggest that we can come to know what is right and what is wrong by the use of reason alone. After all, the moral law exists and is reasonable and God has written his moral law on our hearts and given us reason so that we might understand the world he has created. But if there is no God, no moral law, and if nothing exists but material substances as atheists like Nielsen suggest, why should a notion like ‘reason’ bond us to any particular type of conduct? If there is no moral truth to be discovered and if I have to simply choose the moral point of view because that type of life is what I find worthwhile for myself, then the decision is arbitrary, rationally speaking. The moral difference between Mother Teresa and Hitler is roughly the same as the difference between whether I want to be a trumpet player of a baseball player.
Because the naturalist worldview cannot support the real existence of right and wrong, any standard of morality the atheist comes up with is going to be arbitrary. It will simply be his idea of a good way to have some resemblance of morality in an immoral, impersonal, meaningless universe. Often it will also be inconsistent and even contradictory to the naturalist worldview. To see this, all one has to do is ask the question: How exactly does this ethical standard arise naturally from an infinite sea of ever changing material substances?
Taken from "The Godless Delusion" by Patrick Madrid and Kenneth Hensley.