FRiend, that's not the quote.
"When people stop believing in God, they don’t believe in nothing: they believe in anything" — G.K. Chesterton.
He went to describe about how such people start believing in mutually conflicting ideas, and/or change their beliefs every week - its a real tour de force. I think it's found in 'Orthodoxy'.
Actually, my quote was correct and is from one of his Fr. Brown books.
;-)