https://www.psychologytoday.com/blog/the-winner-effect/201207/why-do-decent-people-bully

Great article. Why do people love to hate? Why do decent people bully? Why did 200,000 to 500,000 East German citizens act as government spies? Why would any of you want to be associated with such a vile organization?

“This is the logic of cognitive dissonance – that strange need to keep the ego reassured that what is being done is all right and proper and above all consistent. This is, of course, how bullies work. They pick a victim. They then choose someone in the group who has no strong feelings about the victim—maybe they even like them. The bully then gets that person to do some small tease—something which on its own is trivial, perhaps even mildly funny—like a relatively harmless comment directed at Karen Klein.

Cognitive dissonance means that they will find it hard to say no when the bully escalates and—implicitly or explicitly—asks them to do something a little bit less innocent, like the more hurtful comments in the escalating abuse of Karen Klein. The dissonance conflict detectors respond in this sort of way: ‘I’m a good person, but I am doing this to them—ergo, they must be a bad person deserving of this.”

So, X is a good person and X is going along with it, so it must be okay. So is X from a certain religious group (many to chose from) and believes this information it must be true, right? How many Xs are out there? Oh X from this group is a good person and knows this about the target, so it must be true and all these people are treating the target in this manner so it must be the right thing to do.