The cardinal sin, when we are looking for truth of fact or wisdom of policy, is refusal to discuss, or action which blocks discussion.

"The Ethics of Controversy", The New Leader (February 1, 1954), reprinted in Philosophy and Public Policy (Southern Illinois UP, 1980), p. 192, and in Sidney Hook on Pragmatism, Democracy and Freedom: The Essential Essays (Prometheus Books, 2002), pp. 294–295