Darwin, in an 1873 letter to his son regarding the best way to oppose Christianity:
“Last night Dicey and Litchfield were talking about J. Stuart Mill’s never expressing his religious convictions, as he was urged to do so by his father. Both agreed strongly that if he had done so, he would never have influenced the present age in the manner in which he has done. His books would not have been text books at Oxford, to take a weaker instance. Lyell is more firmly convinced that he has shaken the faith in the Deluge far more efficiently by never having said a word against the Bible, than if he had acted otherwise….I have lately read Morley’s Life of Voltaire and he insists strongly that direct attacks on Christianity (even when written with the wonderful force and vigor of Voltaire) produce little permanent effect: real good seems only to follow the slow and silent side attacks.”
~qtd. in Himmelfarb 1962, 387.
Source: Himmelfarb, Gertrude. 1962. Darwin and the Darwinian Revolution. New York: W.W. Norton, qtd. in The Darwin Effect: It’s Influence on Nazism, Eugenics, Racism, Communism, Capitalism & Sexism by Jerry Bergman, Green Forest AR: Master Books, 2014, page 343.