thanks this is something I think about a lot. I didn't get too much out of it though, other than the greeks influencing the romans comparison.
"American" culture = White culture
Black people had just a much if not more influence in shaping the actual American culture than whites. Do you think white people mean us when they say "American culture"?
So in their eyes, non-white immigration is a threat to "American culture" (read white influence).