Here’s a purely self-interested rationale for affirmative action in hiring.  An organization repeatedly considers candidates for employment.  A candidate is either good or just average and there are minority and non-minority candidates.  The quality of the candidate and his race are observable.  The current members decide collectively whether to make a job offer to the candidate.

What’s not observable is whether the applicant is biased against the other race.  A biased member prefers not to belong to an organization with members of the other race.  In particular, if hired, he will tend to vote against hiring them.

Unbiased non-minority members of such an organization will optimally hold minority applicants to a lower quality standard, at least initially.  The reason is simple.  An organization with no minority members will have their job offers more often accepted by biased non-minority candidates who will then make it harder to hire high quality minority candidates in the future.  Since bias is not observable, affirmative action is an alternative instrument to ensure that the organization is not hospitable to those who are biased.

The effect is weaker in the opposite direction.  Even if there are minority applicants who are biased in favor of minorities, their effect on the organization’s decision-making will be smaller because they are in the minority.  So at the margin there is a gain to practicing at least some affirmative action.

(This also explains why every economics department should have at least one structural and one reduced-form empirical economist.)