Many of the highly-respected people in academia had fled by the time Hitler came to power, or did shortly thereafter. Vocal critics of the Nazi party who weren't able to escape were mostly thrown in concentration camps, while others were threatened into silence by the brownshirts. The Nazis moved very swiftly after gaining power to prevent those in academia from speaking out, partially by forcing them to become Nazis, and partially by threatening/jailing those who continued to oppose the regime.

For more information on this period in history, I'd highly suggest you take a look at the second book in the Richard Evans Third Reich series, The Third Reich in Power.