Frankl was a Holocaust survivor and Professor of Neurology and Psychiatry at the University of Vienna Medical School:
I became acquainted with the last stages of corruption in my second concentration camp in Auschwitz. The gas chambers of Auschwitz were the ultimate consequence of the theory that man is nothing but the product of heredity and environment—or, as the Nazis liked to say, of ‘Blood and Soil.’ I am absolutely convinced that the gas chambers of Auschwitz, Treblinka, and Majdanek were ultimately prepared not in some Ministry or other in Berlin, but rather at the desks and in the lecture halls of nihilistic scientists and philosophers.
Source: Viktor E. Frankl, The Doctor and the Soul: Introduction to Logotherapy, 1982, p. xxi.
On some of those philosophers: My Nietzsche and the Nazis: print and e-book via Amazon, audiobook at YouTube. On intellectual developments in Germany in the two generations leading up to the Nazis. My recent conversation at Triggernometry, Why They Loved Hitler.