Atheists and pagans object to the penal substitutionary theory of the atonement, mocking it as "divine child abuse," "unjust and immoral," and "Christian foolishness." 1 Corinthians 1:18-25. For some nonbelievers, this is the reason why they reject Christianity. So, Christians who refuse it have this in common with all non-Christians. The penal substitution atonement is approximately 2000 years old -- dating back to when Jesus died on the cross suffering the punishment for sin that we deserved. Obviously our understanding of this work grows each passing year with the development of systematic theology, but Jesus's finished work on the cross is not "new." It is no newer than Galatians 3:10-13, Isaiah 53:5-6, 10, Romans 5:8-10, Romans 3:25-26, etc. etc.
But this thread is not about atonement theories -- we have all seen enough of those thread, and that ground is well trodden. This thread is about C.S. Lewis and the fact that he would refuse God's commands before refusing C.S. Lewis's opinion of good and evil if they conflicted.
C.S. Lewis would refuse to unreservedly say to God "Thy will be done." C.S. Lewis believed that we were not obligated to obey biblical commands that appear to us to be evil. "The ultimate question is whether the doctrine of the goodness of God or that of the inerrancy of Scriptures is to prevail when they conflict. I think the doctrine of the goodness of God is the more certain of the two. Indeed, only that doctrine renders this worship of Him obligatory or even permissible." (C.S. Lewis's letter to John Beversluis, dated July 3, 1963.)
Christian theology has always stood by the teaching that truth is true because God says it is true, and right is right because God says it is right. It was Socrates the pagan philosopher who insisted that he wanted himself to be the ultimate judge of the nature of piety, and that he did not care what God said about it. Euthyphro. Lewis is quite right in stating the issue between Christianity and non-Christianity in the terms he uses. He is, however, quite mistaken when he chooses the side of paganism against Christianity.