WASHINGTON – College campuses are historically safe places for free speech. But many of those so-called homes of higher learning are bowing to censorship.

Free speech advocates warn the growing movement to shut down certain speakers and opinions on college campuses threatens First Amendment rights.

Berkeley was ripped up in February 2017 by rioters who didn't want a commentator from the conservative Breitbart website to speak on campus.

Student Mob Causes Concussion, Whiplash

In March 2017, angry students at Vermont's Middlebury campus shouted down and turned their backs on controversial author Charles Murray, who some label a racist.

Then Middlebury Professor Allison Stanger was assaulted as she helped Murray push through a student mob.

"I suffered a concussion and whiplash," Stanger told CBN News. "Somebody pulled my hair and body-slammed me in the oppositeJeff Sessions was allowed to speak. His topic, ironically enough: attacks on free speech at US colleges.

Students at Washington's Evergreen State College basically forced Professor Bret Weinstein to resign when he wouldn't endorse an April 2017 day of No Whites on Campus and then refused to apologize.

Students Hiding Behind Locked Doors to Talk Politics

Now the schools themselves are buying into the trend. The University of Michigan has what critics assert is an incredibly vague speech code and roving Bias Response Teams.

More than 230 colleges have fielded such teams on their campuses. Michigan's has investigated more than 150 reports of "expression of bias" since it formed up in April 2017.

Critics say these teams intimidate many students, who worry they'll be punished if their words are judged to be politically