People tend to forge their identities when they feel inadequate about their past. As an immigrant privy to no Americans present get-togethers, I see it all the time. The same people who lump all Southerners or Midwesterners into a overweight, bible thumping yokel stereotype, will froth at the mouth about Americans' ignorance of latest political discourse in their small corner of the world. People from predominantly white countries will claim that the US is less cultured because there is too much brown immigration. People who didn't have toilet paper back home will talk about the lack of museums. And so on and so forth.

My personal observation is, the majority tend to forget all the bad and remember all the good about their former home, and conversely, pick out all the bad and none of the good of their new home. It may be hard for you to believe because you are a rationalist, but it's very common.