I have found more cites suggesting it is from the book you said, though I have not found anything suggesting the allegory you describe.
But the analogy is not that far off.
I forgot to say earlier that even if it was meant as an allegory for something else, it still tends to suggest that Lewis's opinion (on the question RR poses in this thread) is that holding on to only the romance is not advisable.
holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)