Unless every single person involved in the holocaust was a psychopath with no capacity for empathy (i know many if not most of them were) i have difficulty understanding how an entire state of people could be capable of such a massive atrocity. How did the Nazis manage to dehumanise the Jewish people and other groups so much that mass extermination could be seen as an acceptable option? Did they manage to convince even otherwise normal people?
The Final Solution underwent many different forms and changes before we finally arrive at the terrible conclusion that takes the form of the death camps like Auschwitz and Treblinka, and much of what was done to exclude and expel the Jewish people (among others) from pre-war German life, like the 1935 Nuremberg Laws, laid the groundwork for greater, more extreme measures to be taken during the war itself. As the Nazi state become much more emboldened and the SS began to assume more of a direct responsibility in physically eliminating "undesirables" in initiatives such as the T-4 euthanasia program and the deployment of Einsatzgruppen during the invasion of Poland, created the blueprints for much of methods used in the death squads and camps in Russia, such as the use of gas vans. This set a precedent of what was capable, and permissible, in the East in regards of extermination of enemies of the state, and launched the Final Solution into it's final phase in 1941/42 from the forced emigration of Jews from Europe into ghettos to extermination.
In terms of how the Nazi's made this awful notion of the persecution of an entire people not only acceptable but considered an ideological imperative, a staple of Hitler's racial ideology on the grounds that the existence of a Jewish conspiracy threatened Germany, and what role the ordinary German person played in purporting this idea is the subject of much debate. By the time World War 2 began, the German people had been subject to 6 years of state anti-Semitic propaganda, which waxed and waned in it's ferocity, occasionally bursting out into violence like at Kristallnacht in 1938, which did much to dehumanize and degrade the Jewish people. This highly charged environment, combined with greater autonomy the SS received in the resolution of the Jewish question in 1941, with a highly motivated and highly anti-Semitic leadership at it's core and with the support if not the official blessing of Hitler himself, allowed for the Holocaust to occur.
Sources: "Hitler, the Germans and the Final Solution" by Ian Kershaw 2008