“Disavow anyone who provokes or accepts the extermination of a race to which he does not belong.”

Preface; Previous Attempts Miss the Point.
1930s, On the Rocks (1933)
Context: The extermination of what the exterminators call inferior races is as old as history. "Stone dead hath no fellow" said Cromwell when he tried to exterminate the Irish. "The only good nigger is a dead nigger" say the Americans of the Ku-Klux temperament. "Hates any man the thing he would not kill?" said Shylock naively. But we white men, as we absurdly call ourselves in spite of the testimony of our looking glasses, regard all differently colored folk as inferior species. Ladies and gentlemen class rebellious laborers with vermin. The Dominicans, the watchdogs of God, regarded the Albigenses as the enemies of God, just as Torquemada regarded the Jews as the murderers of God. All that is an old story: what we are confronted with now is a growing perception that if we desire a certain type of civilization and culture we must exterminate the sort of people who do not fit into it. There is a difference between the shooting at sight of aboriginal natives in the back blocks of Australia and the massacres of aristocrats in the terror which followed the foreign attacks on the French Revolution. The Australian gunman pots the aboriginal natives to satisfy his personal antipathy to a black man with uncut hair. But nobody in the French Republic had this feeling about Lavoisier, nor can any German Nazi have felt that way about Einstein. Yet Lavoisier was guillotined; and Einstein has had to fly for his life from Germany. It was silly to say that the Republic had no use for chemists; and no Nazi has stultified his party to the extent of saying that the new National Socialist Fascist State in Germany has no use for mathematician-physicists. The proposition is that aristocrats (Lavoisier's class) and Jews (Einstein's race) are unfit to enjoy the privilege of living in a modern society founded on definite principles of social welfare as distinguished from the old promiscuous aggregations crudely policed by chiefs who had no notion of social criticism and no time to invent it.

Hymn

The Problem of Anxiety (1925)
1920s

Original: La donna che non provoca alcuna discussione non ha alcun interesse per te.
Source: prevale.net

Letter to George Sylvester Viereck (21 April 1926), quoted in John C. G. Röhl, Wilhelm II: Into the Abyss of War and Exile 1900-1941 (Cambridge: Cambridge University Press, 2014), p. 1237
1920s

Alternate translation: He who boasts of his descent, praises the deeds of another (translator unknown).
Hercules Furens (The Madness of Hercules), lines 340-341; (Lycus).
Tragedies

Misattributed

Gryll Grange, chapter XIX (1860).

A characteristic saying of Russell, reported by Aldous Huxley in a letter to Lady Ottoline Morrell dated 8 October 1917, as quoted in Bibliography of Bertrand Russell (Routledge, 2013)
1910s