“The topic of racial variation is admittedly disturbing, and in an ideal world might be passed over in silence, but accusations against whites have made such discretion impossible. The right of the accused to present his case includes the right to raise issues that distress his accuser. A plaintiff demanding damages for a broken leg cannot ask at the same time that his leg not be talked about, nor take offense when the defendant presents evidence that the injury was congenital. By claiming harm he opens the question of why his leg is game. Claiming racial harm has opened the topic of race differences. “