People are missing Coates' point by trying to focus on the fact that "bitch" doesn't carry the same weight as "nigger." His point is solely about how language is translated and received in intergroup communication. The context in which words are received isn't binary, but rather they contain multiple sliding scales of "offensive" and "not offensive" depending upon those communicating.
When a man is talking, "bitch" is close enough on the "offensive" side of the scale that it is uncouth to use it, but not enough that it has come to commonly be censored as the "b-word" or would be grounds for serious social consequence. When any non-black person is talking, "nigger" is automatically so far close to the "offensive" end of the scale that it has come to gain a censored version and a near-automatic crucifixion of the non-black person saying it.
But again, these distinctions don't actually matter to the point, because he's not talking about where any given word sits on the scale, but the concept of a scale itself. It's about how the context of a word changes depending upon who's speaking it. I mean hell, I'd be willing to bet the majority of black men who choose to use "nigga" amongst themselves would rather be called that than a "bitch." But that's because there's a reclamation context that no other group has experienced with "nigger," much less one that they can lay claim to because they want to act brand new to how communication works.