Affirmative action has reached middle age.

It has been almost 40 years since the US Supreme Court ruled that universities could consider race in admissions as a way to enhance student diversity. Regents of the University of California vs. Bakke (1978) barred schools from giving an advantage to minority students if the purpose was to compensate for historic discrimination against them. The only constitutionally acceptable rationale for affirmative action was to improve the education of all students, who would learn more if they encountered people unlike themselves.

Today, however, Bakke’s vision remains unfulfilled. The problem isn’t just that certain groups continue to be underrepresented, especially at selective universities. Our elaborate rules and procedures for managing diversity are preventing us from realizing its true educational potential.

Recently, the University of Chicago sent a letter to incoming freshmen announcing that they would not receive “trigger warnings” about difficult topics or “safe spaces” to protect them from these subjects. But most of our institutions have embraced the idea that minority students, especially, need to be insulated from insulting ideas. Hundreds of schools have established speech codes barring racist or offensive remarks. They have also invested heavily in student diversity trainings and in multicultural or race-specific “centers,” all aimed at improving the racial climate on campus.

But there’s little indication that these reforms have worked. Most research on diversity trainings in the educational and business world has failed to demonstrate any lasting effect on participants’ racial attitudes. And groups organized around race seem to make their members less comfortable around people of other races.

In a 2008 book examining 2,000 students at UCLA, psychologist Jim Sidanius noted that members of minority-themed campus organizations reported stronger feelings of ethnic identification and also greater levels of political engagement. But he also found that joining such a group increased students’ sense of racial victimization.

So our universities are stuck in a kind of vicious circle. When tensions flare, as they did during the protests that swept campuses last fall, institutions commit resources to minority-related centers and diversity programming. These efforts enhance students’ perception of racism, which in turn generates new demands for institutional action.

That includes speech codes, which have flourished despite court rulings declaring them unconstitutional. According to a 2012 survey of 392 colleges, two-thirds had rules restricting expression that is protected under the First Amendment. For example, Rhode Island College barred “actions or attitudes that threaten the welfare of any of its members.” The University of Northern Colorado prohibited “inappropriate jokes,” which would be funny if it wasn’t so serious.

Or consider the concept of “microaggression,” a centerpiece of many diversity efforts on campus. Its premise is that white people unknowingly offend minorities with remarks like “Where are you from?” or “When I look at you, I don’t see color.” The first comment allegedly highlights a person’s racial difference, but the second one minimizes or ignores it.

So which is worse, or better? When is it OK to inquire about somebody’s background, and when isn’t it? Reasonable people can and do differ on these questions, which is precisely why universities should not be in the business of providing official answers to them. Nor should our universities teach students that their campuses are suffused with unconscious racism, which is -- or should be -- a debatable point as well.

It’s time to scale back our efforts to manage student differences, even as we step up our attempts to recruit different students. Lower-income families need all the financial help we can give them in defraying tuition and avoiding debt, which has reached crisis levels in many parts of the country. What they don’t need are another set of official instructions about race, which alternate between self-laceration (we are racists!) and self-congratulation (we love diversity!)

These exercises run counter to the spirit of Bakke, which warned our universities against establishing dogmas of any sort. Justice Lewis F. Powell’s opinion in Bakke invoked Keyishian vs. Board of Regents, the Supreme Court’s 1967 decision striking down mandatory loyalty oaths for public school and university teachers. “The nation’s future depends upon leaders trained through a wide exposure to that robust exchange of ideas which discovers truth ‘out of a multitude of tongues, (rather) than through any kind of authoritative selection,’” Keyishian declared, in a passage Powell quoted.

On too many of our campuses, diversity itself has become a new kind of loyalty oath. The best thing that has happened at American universities over the last 40 years is the sharp increase in the racial diversity of our students. And the worst thing is the authoritative embrace of singular views about race, which inhibit the multitude of tongues -- and the robust exchange of ideas -- that our differences should bring.

By Jonathan Zimmerman

Jonathan Zimmerman teaches education and history at the University of Pennsylvania and is the author of “Campus Politics: What Everyone Needs to Know.” Readers may email him at jlzimm@aol.com. He wrote this for The Philadelphia Inquirer.

(Tribune Content Agency/The Philadelphia Inquirer)