A Puzzling Thing about American Culture and Racial Identity

As I continue to work on my forthcoming book on racial classification law in modern America, I often notice tangential but fascinating issues.

Here's one. Consider an American who grows up with two white parents, "looks" white, always considers himself white, and assumed all his ancestors were European. He gets into genealogy and in the course of his research discovers that a great-grandfather was a light-skinned, mixed-race-by-descent African-American who "passed" as white and married a woman of European descent. This upends his entire sense of identity. He begins reading up on black history and culture and, over time, starts going out of his way to make black friends, attends a predominately African-American church, and eventually considers himself part of the African-American community and identifies himself as an African American. My sense is that while some people would find this transformation strange, few would consider his new identity fraudulent or illegitimate.

Then consider the case of Rachel Dolezal. She grew up with two white parents, looked white, and so on, but she had adopted black siblings with whom she commiserated, did not get along with her parents, and decided to adopt an identity as an African-American woman. From all accounts I've read, she adopted this identity sincerely, not to game affirmative action or otherwise take advantage of the system. Unlike my first example, she was widely denounced and mocked as a fraud.

I've been puzzling over whether there is some reason beyond racial essentialism (i.e., that your racial ancestry 'matters' in some concrete way, a view generally considered racist) why these cases are different. Is it because Dolezal hid her background? Because she worked for the NAACP and thus took a job away from a "real" black person?

If so, let's say neither of these things were true. Let's say we were talking about James McBride's (The Color of Water--an excellent book, by the way) mother, a white woman who married a black man and, judging from the book, fully integrated into the African-American community. If over time she had come to consider herself an African American, does the fact that she didn't happen to have a black ancestor important? If she discovered that she had a distant African-American ancestor, would that make things different? If so, why?