You may want to read about Dietrich Bonhoeffer and his works - especially Letter and Papers from Prison (available in most librairies, I think and easy to buy); also his collegue Eberhard Bethge wrote the best biography because he was there! There is a new edition but you should be able to get an older edition for very cheap or in a library.
Bonhoeffer, a Lutheran theologian and pastor might have found safety in the US or England (or even Switzerland)where he had job offers. He chose instead to return to Germany and fight Hitler and was hung for having been involved in a plot to assassinate Hitler.
And, it wasn't just the Jews who perished - the Roma people (gypsies); communists, socialists, and anyone else opposed to the regime perished in concentration camps. And, so sure there was apathy. How many people are ever willing to die for their convictions like Bonhoeffer did?
Also, the Nazis first went after other groups:
Do you know Martin Niemoller's quote?
"When the Nazis came for the communists,
I remained silent;
I was not a communist.
When they locked up the social democrats,
I remained silent;
I was not a social democrat.
When they came for the trade unionists,
I did not speak out;
I was not a trade unionist.
When they came for the Jews,
I did not speak out;
I was not a Jew.
When they came for me,
there was no one left to speak out."
So, in short, the Nazis went after anyone interested in opposing fascism and organized enough to oppose fascism before they went after the Jews, if this quote is accurate. As Niemoller was there, went to jail and it is a self-criticism I assume it is true. And, by the way, this is how the Iranian clerics consolidated their power in what had originally been a broad-based social revolution - they destroyed all serious, organized opposition.
You may also find some clues in Abram Leon's book "The Jewish Question" written by a socialist Jew who perished in Auschwitz.
Recently I read that in the post World War I period many rich people in Germany fled to Switzerland to hide their money to avoid paying reparations in the post-war period. While this was in a historical novel I suspect it true. Switzerland continues to play this role today. And, this not only made Germany more unable to pay post-war reparations and exacerbated economic crisis through loss of capital, but perhaps made many small Jewish merchants appear wealthier than they actually were. Wealth and poverty is often relative - compared to one's own state.
And, remember too that Fascism occurs when capitalism is in crisis so many people would not oppose it for that reason.
I recently read that the American pilot Linbergh admired Hilter's regime because he said that in the period after the 1929 crash that it was only in Germany that people were working and had jobs. Since Eisenhower coined the word around 1960 we call this the military-industrial complex in the US. So, Hitler created industrial jobs for his military machine and most people are more concerned with supporting themselves and their family than ideology. Bonhoeffer was well to do and unmarried which made it easier. Hitler also promised each family a "people's car" the Volkswagen made by his friend Porshe. He failed to deliver on this because of the war. But, it was a promise.
Also, of course there is the issue of Hitler and what sociogists call charismatic personality. And, although Hitler could only arise in a certain socio-economic context of capitalism in crisis this may be an angle worth examining.
Some sociologists- especially refugees of Nazi Germany- talked of mass hypnosis in the 1950s- in an attempt to explain what happened.
Although this fell into disfavor in sociology I think you might see what elements of this might be true and how by looking at the Trance Research web site at www.trance.edu
And, what are we doing to stop atrocities small and large these days? How easy is it for us? Are we willing to die matyred over what is right?