On the unifying force - Toni Morrison on November 14, 2016 in The New Yorker:

'This is a serious project. All immigrants to the United States know (and knew) that if they want to become real, authentic Americans they must reduce their fealty to their native country and regard it as secondary, subordinate, in order to emphasize their whiteness. Unlike any nation in Europe, the United States holds whiteness as the unifying force. Here, for many people, the definition of “Americanness” is color.'

(...)

'William Faulkner understood this better than almost any other American writer. In “Absalom, Absalom,” incest is less of a taboo for an upper-class Southern family than acknowledging the one drop of black blood that would clearly soil the family line. Rather than lose its “whiteness” (once again), the family chooses murder.'

Read the article here.

Unlike any nation in Europe?

But history proves Faulker and Morrison right: incest is okay, racial impurity isn't.