This question has been tackled by many persons inquiring into the mechanism of trivialization of evil. Simon Wiesenthal struggled with it on the pages of The Sunflower . The neighbors are watching us. The watching of neighbors, who constituted an unthinking mass, made easier the stifling of the voices of consciousness, at least in the short run. It erases the nature of the personal responsibility of those who could effectively proclaim the ideology of hatred, taking advantage of the convenient indifference of their closest environment.
Situations exist in which the psychologically easy indifference turns out to be a crime.
To be able to derive some precepts from the painful spread of barbarism it is necessary to hold the moral responsibility of the individual above the anonymous mentality of the mob wherein, instead of moral values, emerges the thoughtless copying of the conformism of our neighbors. Acceptance of barbarism can touch average people, who by no means intend to justify genocide or destroy humanistic culture. Wiesenthal recalls specific SS men who loved the music of Bach, Grieg and Wagner. It didn't arise either from simple contempt of the cultural heritage of Europe. It took a much more refined shape in which the defenders of the maniacal ideas could even sometimes portray themselves as intellectuals, citing intellectual philosophers regarded as symbols of courage and creative exploration of new avenues.