This article from The Nation provides some valuable historical context for US society's shift away from social justice to "diversity" as the rationale for affirmative action by intentionally ignoring the reality of systemic racism (h/t Adam Jacobs). Here's an excerpt:
The Bakke ruling shifted the rationale for affirmative action from reparation for past discrimination to promoting diversity. This, in essence, made the discourse about affirmative action race-neutral, in that it now ignores one of the key reasons for why we need to give an edge to minorities. Today the University of Texas, Austin, when defending the consideration of race and ethnicity in admission decisions, cannot say that this practice is needed because of persistent racial inequality; because minority students do not have the same life chances as white students; because there is extensive racial discrimination in the labor and housing markets; because students who study in poor high schools have less chances for learning and lower achievements; or because growing up in poverty impedes your cognitive development. The only argument at the disposal of UT Austin in defense of its admission practices is that it needs a diverse student body to enrich the educational experience of privileged white students.
The full story is told in the book In Pursuit of Fairness by Terry H. Anderson for the history buffs among my readers. I read the book last year, and while it didn't have any real suspense or major revelations, it did help paint a very useful historical picture of how affirmative action has been systematically dismantled over the past four decades. It was no accident, and the arguments you hear from ostensibly liberal professors about affirmative action in admissions and hiring today is the same language used by the likes of Scalia as far back as the 70's (or Scalia today).