Does teaching Holocaust make us hate modern Germany? Does teaching about Pearl Harbor makes us hate modern Japan? Why do they think that teaching black history is exclusively spreading hate?
Because they don’t see the racist, slave-holding south as a past entity separate from their current reality.
If the federal government weren’t stopping them, they’d re-enslave people today. In fact, they have via the prison system. So they don’t want anyone closely examining it, hence banning or slowing the subject in schools if they’re able.