I think you've misunderstood what the author is expressing. From this POV, the article isn't about the divide between black people and white people. The article is about the issue of white identity and the impact that issue has on the ability of humanity to move past race relations. His argument is merely framed by examples of the black vs white struggle which as you rightfully claimed is rooted in descendants of slaves vs descendants of slave owners.
Interesting that you've used another "default", that of maleness. The author is female. None of us is immune, it seems ;) His argument is merely framed by examples of the black vs white struggle which as you rightfully claimed is rooted in descendants of slaves vs descendants of slave owners.
nope, we aren't. We just try to be better. [Also why I've been trying to intentionally not use possessive and gendered language as much as one can. It's amazing how hard it is to break a habit you never really considered until a certain moment in time.]