In the early 20th century, Edmund Landau, a German Jew, championed the position that Pi/2 should be defined as the smallest positive zero of the cosine function. (The cosine itself can be defined as an infinite series.)
For his efforts, Landau was singled out by Ludwig Bieberbach in his inflammatory talk on "J-type" and "S-type" mathematics in 1934. "Thus... the valiant rejection by the Gottingen student body which a great mathematician, Edmund Landau, has experienced is due in the final analysis to the fact that the un-German style of this man in his research and teaching is unbearable to German feelings. A people who have perceived... how members of another race are working to impose ideas foreign to its own must refuse teachers of an alien culture."
Bieberbach started his own journal, "Deutsche Mathematik" to publish "Aryan mathematics".
British mathematician G.H. Hardy published a note in Nature, stating: "There are many of us, both Englishmen and many Germans, who said things during the War which we scarcely meant and are sorry to remember now. Anxiety for one's own position, dread of falling behind the rising torrent of folly, determination at all costs not to be outdone, may be natural if not particularly heroic excuses. Prof. Bierberbach's reputation excludes such explanations of his utterances; and I find myself driven to the more uncharitable conclusion that he really believes them true."
It's striking how apologetic the tone is for failing to find a charitable interpretation of Bierberbach's anti-Semitism. The split between intuitionistic and mainstream mathematics persists today, in less racially charged form. But there are plenty of other divides where it seems like the search for an exculpatory frame of mind obscures the real harm being wrought.
(Quotes from "Numbers", H.D. Ebbinghaus et al, translated by H.L.S. Orde.)