Self-Defense and the Mistaken Racist

How should the law respond when one person (D) kills another person (V), who is black, because D believes that V is about to kill him, but D would not have so believed if V had been white? Should D be exonerated on grounds of self-defense? Some commentators argue that D's claim of self-defense should be rejected. He should be convicted and punished. I argue, however, that denying D's claim of self-defense would be at odds with the principle that criminal liability and punishment should only be imposed on an actor if he chooses to cause or risk causing a harm when the law does not permit him to make such a choice, and not for possessing or choosing to possess racist or otherwise illiberal beliefs or desires. Moreover, insofar as this principle can fairly be characterized as one to which a liberal state must adhere, then a liberal state should acknowledge D's claim of self-defense.