This is a familiar theme among Chesterton readers who know, for example, his quote wherein he declares: "Paganism was the biggest thing in the world, and Christianity was bigger and everything since has been comparatively small." It was a big theme in his book, The Everlasting Man.
It's not surprising that C.S. Lewis also addresses the issue, as one of my students recently pointed out in a term paper. Quoting from C.S. Lewis and Don Giovanni Calibria, The Latin Letters of C.S. Lewis (South Bend, IN: St. Augustin's Press, 2009), p. 90, he writes (first in the Latin, then the English translation):
Hinc status pejor quam illum statum quem habuimus ante fidem receptam. Nemo enim ex Christianismo redit in statum quem habuit ante Christianismum, sed in pejorem: tantum distat inter paganum et apostatam quantum innuptam ed adulteram. Nam fides perficit naturam sed fides amissa corrumpit naturam.Related: Peter Kreeft, "Comparing Christianity & The New Paganism" (www.peterkreeft.com)
This [present] state is worse than that state which we had before the faith [was] received. For no one from Christianity returns into the state which he had before Christianity, but into a worse one: pagans and apostates differ as much as an unmarried [woman] and an adultress. For faith perfects nature, but faith lost corrupts nature.