In Foreign Policy, Stephen Walt writes
In that particular class, Craig argued that one of the many forces that doomed the Weimar Republic was the irresponsible behavior of both left-wing and right-wing intellectuals. The German left was contemptuous of the liberal aspirations of the Weimar Constitution and other bourgeois features of Weimar society, while right-wing "thinkers" like Ernst Junger glorified violence and disparaged the application of reason to political issues. So-called "liberal" intellectuals saw politics as a grubby business unworthy of their refined sensibilities, and so many just disengaged from politics entirely. This left the field to rabble-rousers and extremists of various sorts and helped prepare the ground for Nazism. (You can read Craig's account of this process in his book Germany 1866-1945, chapter 13, on "Weimar Culture").via 3 Quarks Daily
The lesson I took from Craig's lecture was that when intellectuals abandon liberal principles, disengage from politics, and generally abdicate their role as "truth-tellers" for society at large, it is easy for demagogues to play upon human fears and lead a society over the brink to disaster.