First amendment compulsion

Today's Chicago Tribune reports on the agonizing decision of a chancellor to invite a febrile professor to speak.

MADISON -- A Colorado professor who once compared some World Trade Center victims to a Nazi war criminal will be allowed to speak at the University of Wisconsin-Whitewater next month, a decision the chancellor said was repugnant but necessary under 1st Amendment principles of free speech.

There is something I don't understand. Isn't this situation akin to editing? If I publish a journal I can exercise editorial judgment and control. The first amendment does not compel me to publish every article that gets submitted. Likewise, would the chancellor feel compelled under the first amendment to invite every unsavory character that comes down the pike? The usual characters come to mind.