Before Hitler and the Nazi's Third Reich, there was the belief that Germans came from pure barbarian blood. They believed for a long time that their racial purity was being "poisoned" by lesser beings (sub-humans) such as Jews. The belief "One Folk, One Reich" was a means of entrenching the thoughts of racial superiority of the group and the individual superiority of the leader. While the Nazi ideology was vicious, racist and catastrophic, the roots of it dated to before the first world war. In the previous post concerning Kaiser Willhelm, the hatred and scapegoating of Jews was even then old.
Leading up to the outbreak of World War II, the loss of WWI was utilized as a "reason" for the "necessity" of the Third Reich - basically another mythologized bit of propaganda that filtered throughout most of the country.
Hitler was adept at oratory, attuning to the zeitgeist, and at "selling" the Nazi ideology. But the foundation for all of these things was already there. Hitler didn't cause the Holocaust, the workings for such evil were already present in the Reich; but the Fuhrer and his Ministers and Generals were able to take a seed and grow a jungle of hate quite quickly and seemingly easily.
Stopping the spread of malignant propaganda ought to prevent such easy adoption of hateful ideologies. If it happened there, it can probably happen anywhere. And it may not be Jews who are slated for genocide (because there have been other ethnic cleansing conflicts across the world before and since then).
