I like your Nigerian adoptee example. Let’s get away from what he is called and what he calls himself. How does he think about himself? How do various “mixed” individuals think of themselves? To what degree are his adoptive parents ethically obligated to provide with an opportunity to learn about and to identify with his Nigerian heritage? To help him identify with and learn about Black American heritage?
These are issues of personal relevance to me. My youngest child is adopted from China. She is Jewish by vitue of conversion and will be by way of religious upbringing and being raised in whatever aspects of Jewish culture are inherent in our household. (“White” culture is a nonissue to me, I don’t know what that would mean.) I do feel an obligation to provide opportunities for her to develop a positive Chinese identity and know that she will run into some of the very same problems that you describe in your hypothetical: she will be percieved as Chinese first and her Jewish identity will be questioned, yet she won’t fit in with Chinese culture no matter how much I try to give her exposure to it. These are the sorts of issues that I am trying to get at, in the general, from the specifics of Black/White.