A similar event at UC Davis was also canceled.
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The 32-year-old Greek-born British journalist is a senior editor for the conservative news and opinion website. He's been called a spokesperson for the so-called "alt-right" movement for his extreme views on Islam, social justice, and political correctness.
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He's a self-proclaimed "internet troll" who has been widely criticized for being racist and misogynistic.
Passions started flaring around 4pm between both sides on the Cal campus ahead of Yiannopoulos' 8pm speech. The event is sponsored by the Berkeley College Republicans. Extra police officers were called to monitor the event.
The protests turned violent shortly before 5 p.m. as the event approached, with demonstrators lighting fires and fireworks on the Cal campus.
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Yiannopoulos spoke Monday night at Cal Poly in San Luis Obispo, where he drew a diverse crowd of opponents and supporters. Cal State police monitored the crowd closely. The sold-out event was sponsored by the Cal Poly chapter of the College Republicans and not by the university itself.
The barricades were up for the crowds expected ahead of Yiannopoulos' speech before protesters tore them down.
"We're doing this because we feel like we want to exercise our free speech," said President of the Berkeley College Republicans Jose Diaz. "We want to bring someone here on campus to help speak on issues that sort of opens the dialogue."
But there are many others who believe Yiannopoulos' rhetoric is hateful, even dangerous, and has no place on a public university campus.
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"Chancellor Dirks in his statement said the Constitution does not allow him to restrict free speech, and that's not true," said protest organizer Mukund Rathi. "Universities restrict free speech all the time for educational and security reasons."
Last month, Yiannopoulos' planned appearance at U.C. Davis was canceled at the last minute due to security concerns.
Yiannopoulos responded on Facebook after the event was cancelled, saying he had been "evacuated from the UC Berkeley campus after violent left-wing protestors tore down barricades, lit fires, threw rocks and Roman candles at the windows."
"We are confident that we have the plan and the pieces in place," said Dan Mogulof of U.C. Berkeley. "The law, ample court precedent, and the Supreme Cout could not be clearer that this event is fully and completely protected by the first amendment."