so where is the rule that prevents people from speaking that you claim exists?
It's in the article. It's pretty clear. The universities have set up rules about speech codes and the like. They get to determine what is appropriate and the language of the codes are vague and broad. Thereby granting them broad discressjon in what they call 'hate' or 'violen' speech.
Back when Anne Coulter was doing speeches at college she was always heckled. She was assaulted, more than once. Students would gather to shout out her speech, and she was even barred from speaking at some after she was announced as the speaker.
I'm not a Coulter fan. But she's published and does well and she has a right to her opinion, but more than that I have a right to hear her opinion if I choose. All those people stopped not just her speech, but the rights of all those who wanted to hear her.