I completely agree with the "You're all American, period" sentiment, but I suspect you haven't had the lovely experience of being asked "Where are you from" and have your <American location> repeatedly not accepted, usually by the phrase "No, where are you really from," as if it's entirely impossible for me to have been born here.

Were I white, the first question would be unlikely to be asked in the first place, its answer automatically accepted, and if the enquirer had poor language skills, it would immediately be qualified with "I meant, What's your heritage" or "Where is your family from."

There may be self segregation but some are doing the segregation for us.