The fundamental difference between the liberal and the illiberal outlook is that the former regards all questions as open to discussion and all opinions as open to a greater or lesser measure of doubt, while the latter holds in advance that certain opinions are absolutely unquestionable, and that no argument against them must be allowed be heard. What is curious about this position is the belief that if impartial investigation were permitted it would lead men to the wrong conclusion, and that ignorance is, therefore, the only safeguard against error. This point of view cannot be accepted by any man who wishes reason rather than prejudice to govern human action.
-Bertrand Russell, “Freedom and the Colleges,” The American Mercury, May 1940, pp. 24-33.