Martyrdom has always been a proof of the intensity, never the correctness, of a belief. – Arthur Schweitzer, Out of My Life and Thought, 1932

We are all tattooed in our cradles with the beliefs of our tribe; the record may seem superficial, but it is indelible. You cannot educate a man wholly out of the superstitious fears which were implanted in his imagination, no matter how utterly his reason may reject them. – Oliver Wendell Holmes, Sr., The Poet at the Breakfast Table, 1872

Not… what opinions are held, but… how they are held: instead of being held dogmatically, [liberal] opinions are held tentatively, and with a consciousness that new evidence may at any moment lead to their abandonment. – Bertrand Russell, Unpopular Essays, 1950