A fanatical group all together have a comfortable feeling that they’re all friends with one another. They are all very much excited about the same thing. You can see it in any political party. There’s always a fringe of fanatics in any political party, and they feel very cozy with one another; and when that is spread about and is combined with a propensity to hate some other group, you get fanaticism well developed.

Bertrand Russell (1872–1970) English mathematician and philosopher

Interview by Woodrow Wyatt, BBC TV (1959)
    (Source)

Collected in Bertrand Russell's BBC Interviews (1959) [UK] and Bertrand Russell Speaks His Mind (1960) [US]. Reprinted (abridged) in The Humanist (1982-11/12), and in Russell Society News, #37 (1983-02).