I agree that a good book is a good book, no matter the ethnicity of the author. If a white author can write a book with mainly black characters, making them multi-dimensional rather than stereotypical, then I don't see it as a problem. However, it would be wonderful to see the day when black authors can write books dominated by white characters and have their books accepted in the mainstream. Then we'll know we've made progress.
Black authors are usually forced to write only about black characters, with a few rare exceptions; otherwise, their books won't get picked up by major publishers. I'm sure there are exceptions to this rule, but none readily come to mind. Perhaps Troy can think of a few. When I think of the fiction writers who have had major breakthroughs -- Terry McMillan, Walter Mosley, Carl Weber, Toni Morrison, Alice Walker, Stephen Carter (who may be the exception) -- their protagonist is almost always black.
Now, I don't want to take away from the joy found in writing about African American culture. And, as a reader, I appreciate having a large number of books from which to choose that reflect my culture. But writers -- all writers -- should have choices and options. That's what freedom is all about.