We have had 2000 years to evaluate the truth of Christianity. Anyone pretending to find a new argument is deluded.
The OP demostrated that what C.S. Lewis was addressing isn't exclusive to the Christianity. The concept of a transcendent moral conscience, natural law, the Dao, or wherever you want to call it, was accepted in principle by Socrates, Jesus, Siddhartha Gautama, Thomas Jefferson and the Deists, and by Confucian thinkers.