I think black people are more likely to be offended by offensive material than white people are. Not because of any genetic thing, but because racism actually negatively impacts them personally (whereas it positively impacts white people personally), so they are quite understandably more aware of racist aspects to a book and less likely to overlook them. This isn't a defect--quite the opposite, actually; if white people were more attuned to racism the world would be a better place.

(Disclaimer: I am myself white.)