Harden's original name was Witkowski, and although he converted to Christianity at 16 his enemies always attacked him as a Jew. He was originally an actor but from 1892 to 1922 he edited and mainly wrote Die Zukunft, a political, cultural and theatrical weekly. He was an aggressive nationalist at the beginning of WWI but by the end of the war he had become a republican, a pacifist and a socialist. In 1922, Harden was severely beaten by members of a secret anti-Weimar terrorist organization; a beating from which he never quite recovered.
The trial of the terrorists in 1922 demonstrated the hostility of judges toward the Republic, toward socialists, and toward "Jews". Harden told the judges at the end of the trial that if they continued to allow verbal assaults on Jews in the courtroom, Jews might as well be forced to wear "yellow stars".