In 2002, a history professor published an article suggesting that the "No Irish Need Apply" prejudice against Irish immigrants to the 19th Century US was, in fact, a myth, a delusion fostered within the Irish-American community to promote solidarity around victimization. As the most scholarly article on the subject, it actually got a fair amount of traction.
Until last month, when a high school student actually did some research into newspapers and want ads of the era and found lots of evidence that NINA was not rare but actually pretty widespread.
The sad thing is the number of groups that face prejudice and then, when they become accepted, are happy to dole it out again without any sense of hypocrisy. Even if today Irish-Americans (of which I'm one) remember the nativist anti-Irish and anti-Catholic prejudice their ancestors faced (and not-so-ancestor … look at John Kennedy's election for some of the guttering flames of that era), too many of them seem quite willing to turn on the next set of Others, the next immigrants, the next people with a strange religion and an asserted tendency to violence.
Long Island Wins : High School Student Proves Professor Wrong When He Denied “No Irish Need Apply” Signs Existed : Columns
Professor Richard Jensen described Irish Americans as delusional for thinking they had been discriminated against in the 19th Century. Teenager Rebecca Fried proved him wrong in a prestigious academic journal.
One of the emergent properties of a society with a big inequality in power is that the people in power don't actually have to lift a finger to maintain their system, because the people on the bottom will individually benefit so much by betraying other people on the bottom that they'll maintain the structure themselves. A crass version of this is called crab mentality, although it doesn't acknowledge the overall power structure.