The "mismatch" argument against affirmative action.

Explained by Richard Sander and Stuart Taylor Jr.:

The mismatch effect happens when a school extends to a student such a large admissions preference — sometimes because of a student's athletic prowess or legacy connection to the school, but usually because of the student's race — that the student finds himself in a class where he has weaker academic preparation than nearly all of his classmates. The student who would flourish at, say, Wake Forest or the University of Richmond, instead finds himself at Duke, where the professors are not teaching at a pace designed for him —  they are teaching to the "middle" of the class, introducing terms and concepts at a speed that is unnerving even to the best-prepared student.

Read the whole thing. It's odd that these observations are surfacing so late in our experience with affirmative action, but there's a new case pending in the Supreme Court, which creates an occasion for elaborating the policy pros and cons. I remember discussions about affirmative action, back in the 1980s, in which any attempt to make this argument would provoke a sharp rebuke.

With striking uniformity, university leaders view discussion of the mismatch problem as a threat to affirmative action and to racial peace on campuses, and therefore a subject to be avoided. They suppress data and even often ostracize faculty who attempt to point out the seriousness of mismatch.

It's a painful thought, that you are hurting the people you meant to help. The urge to repress ensues. It's much easier to justify imposing a disadvantage on the people you decided could bear the burden. That's something academics have long felt comfortable discussing openly.