Why are culture and identity such contested terrain in contemporary America?

When considering American culture and identity, one could argue that there is no such thing, since contemporary America is home to a cultural and ethnic mix so great that it cannot be considered as a whole; alternatively, American culture and Identity may be seen as an amalgam of social and cultural differences from the many ethnic groups that inhabit this great continent. These two opposing ideas, of a "salad bowl" (the former) and a "melting …

…Open University, Hodder and Stoughton, UK Walker F.A. (1896) "Restriction of Immigration", The Atlantic Monthly; Volume 77, No. 464; 822-829; http://www.theatlantic.com/unbound/flashbks/immigr/walke.htm (last accessed May 17th, 2004) Key Documents, 1924, Immigration Act, 54-57, Chinese Exclusion Act of 1882, http://www.mtholyoke.edu/acad/intrel/chinex.htm, last accessed May 18th, 2004 TV02, viewed on May 9th, 2004, From a Different Shore, TVB Pearl TV01, Viewed on April 18th, 2004, Out of the Melting Pot, TVB Pearl