Another objection to faith that C.S. Lewis struggled with was the question: Aren't morals relative? More than two-thirds of Americans deny any belief in absolutes and the statistics would be very similar in other countries.
An an atheist, Lewis denied that there were any moral absolutes. When he became a Christian, he insisted that Christian morality had to go beyond mere personal opinion. It had to fit with life as a whole, or it was meaningless.
Lewis queried where he got this idea of things being just and unjust. A person does not call a line crooked unless they have some idea of a straight line. An absolute standard of good suggests a God who is the infinite reference point. Lewis went to great lengths to document the universality and timelessness of moral standards. In the appendix to The Abolition of Man he cites the similar moral standards of ancient Egyptians, Babylonians, Hindus, Chinese, Greeks, Romans and others. Though the specifics may differ, the general outline is the same throughout all cultures.
If there is no absolute standard for good and evil (God), there there is no evil. One or the other has to go, either atheism or a major argument for atheism.
The relativistic viewpoint is hopelessly inconsistent. The attempt create an ethic without God is doomed to failure. No relativist who has been given absolute power has used that power benevolently.
[Summarised from Chapter 11 of Art Lindsley's C.S. Lewis' Case for Christ]
Next: Lewis and Other Religions.