The mayor of Berkeley is urging the cancellation of an event bringing right-wing speakers to the University of California, extending a debate about the border between speech and violence.

With a student group working to host right-wing provocateurs Ann Coulter and Milo Yiannopoulos in Berkeley, the liberal haven is contemplating a repeat of violent counter protests that greeted a right-wing rally this past weekend.

“I don’t want Berkeley being used as a punching bag”, Mayor Jesse Arreguin told the San Francisco Chronicle, warning about the risk of “groups using large protests to create mayhem”.

A spokesman for the group putting on the event, the Berkeley Patriot, blasted the mayor's call to halt the event as “absolutely abysmal”.

“We feel the mayor shouldn’t be giving in based on the threats of violence,“ Bryce Kasamoto told The Independent.

In a statement, a spokesman for UC Berkeley said that the university did not invite the speakers and had no authority to halt the planned event.

“We have neither the legal right or ability to interfere with or cancel their invitations based on the perspectives and beliefs of the speakers”, Dan Mogulof said, adding that “the safety of our communities, and the well-being of those who may feel threatened or harmed by what some of these speakers may espouse…along with our commitment to Free Speech, remain at the center of our planning and priorities”.

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An open letter from Berkeley Chancellor Carol Christ encouraged tolerating a range of viewpoints, even those “that most of us would find hateful, abhorrent and odious”.

“The right response is not the heckler’s veto, or what some call platform denial” Ms Christ wrote. “Call toxic speech out for what it is, don’t shout it down, for in shouting it down, you collude in the narrative that universities are not open to all speech”.

Berkeley High School Walkout in protest against Donald Trumps election

But in advocating for the speeches to the canceled, Mr Arreguin has taken the opposite approach. His plea marks the latest effort by Bay Area officials to balance free speech against public safety - with the latter recently winning out.

Ms. Coulter was scheduled to speak at Berkeley earlier this year but the university canceled the talk, with then-chancellor Nicholas Dirks writing of “threats of violence” and warning that “this is a university, not a battlefield”. Students who supported Ms Coulter's speech have since sued the university. Months earlier, the university nixed a scheduled appearance by Mr Yiannopoulos after demonstrators smashed windows and ignited fires.

Prominent San Francisco elected officials mounted a concerted effort to block a right-wing rally last weekend from Crissy Field. The federal Park Service rebuffed their request, saying an organization’s “political stance or beliefs” was not grounds to deny a permit, but the event’s organizer canceled the event at the last minute after blaming politicians for vilifying him.

A “No Marxism in America” event the next day in Berkeley proceeded and spiraled into street brawls as contingents of left-wing protesters, some of them aligned with antifascist organizations that advocate confronting white supremacists with violence, pummeled their perceived opponents.

Assessing the aftermath, Mr Arreguin on Monday told a local CBS affiliate that violent leftist factions should be classified as gangs. That prompted a derisive response from a Berkeley antifascist group.

Prior to the event, the mayor had urged counterprotestors to stay away and warned of groups that “come eager for a fight”. Referring to a neo-Nazi March in Charlottesville, he argued that “this is not freedom of speech - This is bigotry. This is racism. This is xenophobia”.