What and How We Know
The Quotable Bertrand Russell, Lee Eisler, ed. (Prometheus, 1993), p. 106.
It is the things for which there is no evidence that are believed with passion. "Nobody feels any passion about the multiplication table or about the existence of Cape Horn, because these matters are not doubtful. "But in matters of theology or political theory, where a rational man will hold that at best there is a slight balance of probability on one side or the other, people argue with passion and support their opinions by physical slavery imposed by armies and mental slavery imposed by schools.
Proposed Roads to Freedom (H. Holt & Co.), p. 147.
What a man believes upon grossly insufficient evidence is an index to his desires — desires of which he himself is often unconscious. If a man is offered a fact which goes against his instincts, he will scrutinize it closely, and unless the evidence is overwhelming, he will refuse to believe it. If, on the other hand, he is offered something which affords a reason for acting in accordance with his instincts, he will accept it even on the slenderest evidence.