Even "free speech" has limits, and it's not always crying "fire!" in a crowded theater.  I'm sure some in Germany wish Hitler should of been stopped from speaking.  But we don't just turn the other cheek, when someone wants to preach an extremism, not popular among the democracy.  Conservative students are more than welcome to protest and attempt to drive away who they may feel are extreme liberal speakers, but I'm betting they won't be effective?  The fact that protests to stop extreme speakers like Milo Yiannopoulos or Anne Coulter, are sometimes successful, one has to step back and look at the not the intent to stop them from speaking, but who's really listening.  I'm all in favor of letting anyone of such extremism speak openly, because as the saying references, better to remove all doubt of what the speaker really intends.