Nicole Bengiveno/The New York Times The final hurdle: Many more blacks than whites fail to pass the bar examination. ONE would have thought, given the decades of ardent debate over affirmative action in higher education, that the main axes of the dispute had been established. Defenders of racial preferences say that they compensate for historical wrongs, ensure vibrant and varied campus discourse and help create minority role models and leaders. Opponents say preferences are nothing but a reverse form of discrimination that stereotypes and stigmatizes minority students. But a recent study published in The Stanford Law Review by Richard...