I repeat things because others do.

Leiter quotes a brief in the Harvard affirmative action case. 

Shortly after Grutter was decided, the defendant in that case confessed that he had pressed “the ‘diversity’ rationale” as a litigation strategy. Bollinger, A Comment on Grutter and Gratz v. Bollinger, 103 Colum. L. Rev. 1589, 1590-91 (2003). Bollinger bemoaned that he could not defend racial preferences as “a ‘remedy’ for past societal discrimination”—what everyone in higher education “really believed.” Id. Bollinger is hardly alone. Shortly before Grutter was decided, Harvard’s Randall Kennedy said, “Let’s be honest: Many who defend affirmative action for the sake of ‘diversity’ are actually motivated by … social justice.” Kennedy, Affirmative Reaction, Am. Prospect (Feb. 19, 2003), bit.ly/3EJc5To. They would defend racial preferences “even if social science demonstrated uncontrovertibly that diversity (or its absence) has no effect (or even a negative effect) on the learning environment.” Id. NYU’s Samuel Issacharoff likewise knows “‘[t]he commitment to diversity is not real,’” and Columbia’s Kent Greenawalt has “‘yet to find a professional academic who believes the primary motivation for preferential admission has been to promote diversity.’” Fitzpatrick, The Diversity Lie, 27 Harv. J.L. & Pub. Pol’y 385, 395-96 (2003). The list goes on. See id.; Schuck, Affirmative Action: Past, Present, and Future, 20 Yale L. & Pol’y Rev. 1, 34-36 (2002); Levinson, Diversity, 2 U. Pa. J. Const. L. 573, 601 (2000).

I've also argued previously that "diversity" is a weak and implausible rationale for affirmative action. 

Leiter: There's no epistemological need to have blacks, or women, or homosexuals, or Palestinians, tell their own stories, or judge others' stories. 

On affirmative action, constitutional or not—and contra Leiter, there's an argument to be made that strictly speaking it never was—times change.

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To be clear because I've said it before: affirmative action may have been unconstitutional, but it was necessary.