Probably a big factor contributing to all the bystanders during the Shoah was the general state of interfaith relations during the 1940s and 1930s. People generally kept within their own in-groups, and had been taught to view outsiders as alien others. This isn’t true only of Jewish–Christian relations, but also of relations between many other groups. This wasn’t an era of multicultural neighborhoods and schools, a huge rate of interfaith marriages, and committees to discuss local interfaith relations.
Most people live what they know. It’s very hard to break out of our walls and boxes, particularly when we’ve inherited them through the generations. There’s also the threat of opposition from those who think you’re trying to “get above your raising.” These things you’re rebelling against were good enough for your parents, grandparents, and ancestors, so why aren’t they good enough for you?
Until the end of WWII, anti-Semitic attitudes were considered socially acceptable. People didn’t attempt to hide their true feelings. Many other isms and phobias were also widespread and socially acceptable. They didn’t consider themselves hateful or bigots, since they were just living what they knew. This was normal behavior in the context of their culture and era. Most people’s attitudes towards other races and religions didn’t go so far as violent manifestations like lynchings and pogroms. They might’ve “just” thought the races, sexes, and religions were unequal, used epithets, or refused to associate with those they considered lesser. Prior to the era of instant, mass communications, people were much less interconnected.
Generally, unless you lived in a giant, multicultural metropolis or had opportunity or reason to associate with a lot of people outside of your in-group, there was no compelling reason to question what you’d been taught or seek out relationships with these others. For example, it’s like nails on a chalkboard every time I see or hear a woman referred to as “Mrs. Husband’s Full Name,” and can’t understand why that was ever considered anything but passive identification writing women out of existence. However, until a few decades ago, that was just how things were done. Most mainstream folks didn’t consider that disrespectful or sexist. Women who retained their birth surnames were considered the unnatural radicals.
My own paternal grandparents (may they rest in peace) often used the N word, and didn’t understand why it’s racist and offensive. I knew they were good people in spite of certain racist views which were a product of their time. We can’t simplistically dismiss people of bygone eras as unenlightened bigots for going along with attitudes they had no reason to question.
There’s ample, obvious historical evidence of long-standing anti-Semitism in Europe, particularly Eastern Europe. Again, that doesn’t necessarily make these people bad for just living what they knew, but it’s not something we should deny or downplay. I’m not going to stop being a passionate Russophile, Slavophile, or Magyarphile just because of the long history of anti-Semitism in the former Russian Empire, Poland, and Hungary. It certainly doesn’t mean every single person was an anti-Semite, nor that every anti-Semite’s feelings went so far as actively participating in pogroms or the Shoah. It just means there’s a difficult part of that history and culture, which it would be intellectually dishonest to sidestep. History, like science, only cares about facts, not your feelings.
I’ll address this more in other posts, but suffice it to say, acknowledging anti-Semitism and collaboration in a place like Poland, Ukraine, or Hungary doesn’t cancel out how their Gentile populations suffered in their own way under Nazi occupation, nor the many Righteous Gentiles recognized by Yad Vashem. However, let’s not get into the historical revisionism certain people (esp. far-right Polish nationalists) engage in, trying to deny there were ANY anti-Semitism, indifferent witnesses, or collaboration.
The Shoah could not have happened without widespread indifference, collaboration, and anti-Semitism. It was the same reason Jim Crow went unchallenged so long in the U.S., and why so many people didn’t think to question institutionalized sexism until the second wave of feminism in the 1960s.