I'm fully aware that there as Hispanics, Asians, and others who are assimilating quite well into American society and wants to be American and I'm more than happy to have that sort of immigrant enter the United States. Regardless of where it started or how well it worked in the past in the United States, the "Melting Pot" was an admirable goal and far more sustainable than the multicultural ideals being preached by many academics. I'm by no means anti-immigration. I'm anti-multiculturalism to, the extent that many multiculturalists want to take it, and think America needs a single official language. If the people of India can understand the benefits of using English as an official language, despite it being almost nobody's native language in India, why can't Americans grasp the same benefits.
I've spent alot of time speaking with older relatives. Despite the differing ethnicities (Polish on my father's side, Italian on my mother's), a common thread was that the first generation who came to this country never considered themselves "American", while their children largely became Americanized through popular culture and military service. After all, even though the second generation was born here, they nevertheless stayed in the neighborhood and played with other kids of their ethnic and religious background.
I think that popular culture, which is stronger than ever as an influence, position or negative, on today's youth, is the key factor in spreading English and American mores on the children of immigrants. Little Juan, Kim, Vladmir, or Joao may speak the language of their parents at home, but through watching television, going to the movies, listening to the radio, and hanging out in the school yard, they pick up the language very rapidly, despite the multiculturalist propaganda.
My belief is that America does have a unified culture, which is effective on both the conscious and subconscious level. Underneath that culture, there are many subcultures that are related to ethnicity, religion, region, etc. That's the way it always has been and always will be.