Whites in the United States are not responsible for the fact that American Negroes usually are less prosperous than we are. We are responsible for the fact that American Negroes are usually more prosperous than most Negroes in black majority, black run countries. We are not pushing Negroes down; we are lifting them up. Their weight is getting hard to bare.It's not black history, it's American history. No one is saying the focus of teaching history be on racism or slavery, only that those subjects be discussed as accurately and thoroughly as possible.
As far as the "they already know" argument, Americans remain amongst the most ignorant of any industrialized country in the world, so don't assume that anyone knows anything, especially in regards to history.