For left-wingers on college campuses, spring cleaning involves more than dredging their dorms for pizza boxes from October. For at least the past two decades, students have also cleansed (if that's the right word) their commencement ceremonies of speakers with whom they disagree on politics. They've tossed Condoleezza Rice, Alec Baldwin, Christine Lagarde and many others out of the proverbial window along with last semester's late-night Dominoes order.

But commencement speakers are not invited to lecture graduates on their political beliefs, so why do students protest their speeches solely because they disagree with them on politics? If students stopped their protests and listened, they'd probably learn something from people who are there because they have the experience to recount and wisdom to impart.

A petition circulated last spring among liberal Georgetown students urged the university to rescind its invitation to then-Homeland Security Secretary Jeh Johnson, a longtime Democrat and the nation's first African-American Homeland Security secretary, who was slated to speak at the school's commencement ceremony in May. "Johnson's invitation is an insult to my family, to the myriad of Georgetown alumni from mixed-documented families, and to the undocumented students who are preparing to graduate this month," a forlorn alumna lamented. "Graduation is supposed to be a safe, welcoming environment for students and families who have worked so hard to graduate, not a hostile or uncomfortable one."

Johnson spoke, but the petition picked up enough steam to make news in the national media.

At Harvard in 2014, students sought to cancel former New York City Mayor Michael Bloomberg's commencement gig over his support for "stop-and-frisk" policies and heightened surveillance after 9/11. Students at Catholic University of America rejected John Boehner in 2011 because they didn't like his preferred policy solutions to poverty.

Dr. Ben Carson, one of the world's foremost neurosurgeons, was pressured to back out of a commencement address at Johns Hopkins University, where he was retiring as the Director of Pediatric Neurosurgery, over comments about traditional marriage for which he had since apologized.

From George W. Bush to Madeleine Albright to Chief Justice John Roberts, dozens of national leaders have faced frothed-up outrage from students who weigh political beliefs over personal achievements in their litmus tests for speakers.

Consider the cases of Ben Carson and Condoleezza Rice, the latter of whom withdrew from a commencement address at Rutgers over students' concerns about her role in the Iraq War. Neither Carson nor Rice would have spoken to graduates about homosexuality or weapons of mass destruction. In fact, they probably wouldn't have spent any time on political issues at all.

Instead, they would have shared thoughtful advice gleaned from their experiences overcoming racism and hardship to achieve historical successes in their respective fields.

What about Michael Bloomberg, who spent more than a decade as the mayor of the largest city in the most powerful country on earth? Or John Boehner, who was the Speaker of the House of Representatives at the time he was protested by students?

University of California, Berkeley students protested then-Attorney General Eric Holder, a staunch liberal and the first black attorney general, because of his position on an issue as minor as medical marijuana.

What does it say about students that they seek to shut out some of the world's most influential world leaders, many of whom have risen from modest means to enormous power? It says that, far from being ready to graduate into the real world, they have used their time at university to imprison themselves in a moral playpen.

After spending four years in courses that serve more as advertisements for liberal ideas than serious learning environments, they want to purge their ceremonial send-off into adult life of any troubling challenge to the certainties they have acquired at the knee of the left-dominated academy.

If, for instance, Rutgers asked students to listen to Condoleezza Rice justify the Bush administration's conduct in the Iraq War, the experience would still be valuable, but protests would also be more reasonable.

To protest a non-political commencement address by one of the nation's most successful African-American and female leaders because of her politics is not only unreasonable. It is symptomatic of a sickness bred in higher education that compels students to blend their newly-developed ideological intolerance into personal intolerance and invalidate the experiences of anyone who falls on the wrong side of that equation.

When someone disagrees with a prescribed doctrine, they are not simply wrong, according to this philosophy, they are dangerous. People, to these disciples of dogma, are only worth as much as their politics.

As that belief proliferates, moving with graduates from campuses to the working world, our collective struggle to connect with people different from ourselves will grow only more strained.