Rosner’s reply is just an artful dodge.

Suppose that when the country was debating the merits of an all-volunteer army, a defender of the draft had said, “Your theory sounds nice, but can you prove that the United States has no more enemies in the world?” Most people, and especially anti-draft liberals, would have seen that as an evasion. Whether or not we had or ever could reach the wonderful state of having no enemies was completely irrelevant to the case for doing away with conscription. Similarly, whether or not we have or ever could reach the state where race doesn’t matter to anyone is irrelevant to the argument over giving racial preferences to select Americans to get into somewhat “better” colleges and universities than they could just on the basis of their academic capabilities.

The burden of proof should be on Rosner and preference advocates to demonstrate that extending racial preferences (to them, “good” discrimination) does anything to reduce “bad” discrimination elsewhere in society. I have never seen any effort to do that.