F4LL0UT: That seems to be what you Americans want your immigrants to behave like.
Not americans, just a certain category of people, and you can find them in every country. Immigration is about integration (how to articulate your identity, practices, customs, background, to the local society). Xenophobia is about uniformity and the eradication of alterity. It takes two complementary shapes : exclusion and assimilation. What is not the absolute same must be either expelled, or transformed into the absolute same, two ways to suppress any difference and restore the fantasy of intemporal national/cultural homogeneity.
You can see this in many contexts, from ordinary xenophobic discourses about the neighbour not listening to the right music or not cooking the right food, to downright assimilationist (ethnocidary) policies towards native populations - a phase that generally overlaps and follows the colonial exterminations. The idea remains the same : the glorification of homogeneity, the horror of heterogeneity. With, in the case of migration, the fear of any influence on society, percieved as a "loss" from the pristine, "pure", popped-from-the-ground, traditional socioculture that is essentially the speaker's vision of his childhood environment, idealized, imagined as eternal (until the transformation he witnesses with terror), and integrated as "normality" (that is : superior to everything else in the world).
Whatever the country or context, once a person starts expecting "assimilation" instead of integration, you know to what family of thought he belongs. But it's not a specifically north-american thing. The USA as a whole are a very, very multicultural place (it has ceased to represent itself as a "melting pot" -the dubious illusion and expectation of fused and erased identities- and switched to the more healthy and realistic image of "salad bowl" - a mix of differences, functioning together), so there isn't more globally normative pressure there than in other places of the world.
It's just the manifestation of what tinyE said about families.