On Tuesday, the University of Minnesota Law School hosted Prof. Moshe Halbertal — a world-renowned philosopher, political theorist and historian of Jewish thought, as well as one of the world's leading military ethicists — who delivered the annual John Dewey lecture in the philosophy of law. I had the pleasure and honor of introducing Prof. Halbertal.

As is now widely known, Halbertal's lecture was delayed some 40 minutes. My colleague, Prof. Dale Carpenter, described the scene in a post he published: "[O]ne by one … protesters stood up to shout denunciations of Israel and were escorted from the hall by university police. One young woman came screaming back into the lecture after having been ejected. Outside the hall, the protesters chanted so loudly that it was difficult to hear Halbertal, much less to concentrate on what he was saying, until 45 minutes after the lecture was to have begun."

These acts of cultural hooliganism present a real threat to free speech and the free exchange of ideas. Carpenter is correct in noting both that "there is no right to shout down a speaker at an academic lecture" and that "members of a university community have an obligation to consider opposing viewpoints and, if not always a duty to listen to them, then at least a duty to allow others to listen to them."

The affront to free speech in the appalling conduct of the protesters should be disturbing to anyone. So too should be the overtly anti-Semitic attitudes demonstrated.

Let me be clear. It is absolutely legitimate to criticize the state of Israel and the policies of its government. I myself have expressed such criticism often. Unfortunately, much of the anti-Israel discourse is but a thin disguise for anti-Semitic sentiments.

To criticize Israel is OK. To call for the utter destruction of the Jewish state and for a Jewish Free Zone between the River Jordan and the Mediterranean Sea, as the protesters repeatedly chanted, is anti-Semitic. To criticize Israel's policies is legitimate. To single out Israel as the only country for such criticism while maintaining a deafening silence (and at times even support) for Arab and Muslim regimes that brutally murder their own citizens and harbor genocidal plans against the Jewish state is anti-Semitic.

It is also important to note that the protests at the Law School were not an isolated incident. They are part of a campaign carried out on campuses across the country designed to intimidate Israel supporters and Jewish students and professors.

Finally, to challenge views, positions and speakers is a mainstay of the academic exercise. But I suspect that had the invited speaker been anyone other than an Israeli and a Jew we would not have seen the protests that we witnessed on Tuesday. The protests occurred because the speaker was an Israeli and a Jew. That, too, is anti-Semitism.

Perhaps, you may think, the protests were not aimed at the speaker because he was an Israeli and a Jew but because of the substance of his positions? Here, too, you are in for a rude awakening. The gist of Halbertal's talk was that soldiers ought to assume significant risks, indeed greater than many military ethicists would argue for, in order to protect noncombatants. Does that sound like an apology for war crimes, as the protesters would have you believe? Indeed, some of the protesters also demonstrated a few days earlier against a rally for peace held on the campus and at which I spoke. Protesting against peace and protesting against greater protection for civilians: Is that the message the protesters wish to convey?

The cultural hooligans who disrupted Halbertal's lecture ought to be condemned in no uncertain terms for their infringement of basic rights and their anti-Semitic message. Moreover, the University of Minnesota must investigate, determine whether any university students violated university policies and, if so, impose appropriate discipline.

A failure by the university to do so will incentivize other groups to disrupt with impunity any speech they disagree with. It will also signal a measure of unacceptable tolerance for hate speech and anti-Semitism.

Oren Gross is Irving Younger Professor of Law at the University of Minnesota Law School. The opinion expressed is that of the author and not necessarily that of the Law School or the university.