A good author does research. We should assume that a White author who writes a non-White character has spoken with, read, observed, digested, and otherwise figured out how to get the character's identity right. ALL of the characters in a novel are NOT the author, so the problem is only one of degree. How does a Steinbeck write a Lenny?

This dust-up is really about turf. There are so few opportunities for authors of color that they need a preserve - a subject that only they can address so that the only way to read about that subject is to BUY the work of an ethnically matched author. A White author who invades colored turf isn't so much being literarily presumptuous as commercially invasive. The argument about competence is silly, but the economics are real, and a straightforward "Get out of our way" sounds like whining. So we get the cultural argument instead.