Law schools restricting Lecturers' speech in class

[Volokh, Eugene]

Any thoughts on whether the proposed policy discussed in this e-mail (which I am told was circulated by the Boalt administration to Boalt law students) is likely to be constitutionally permissible?  Naturally, it would depend on the precise language, but any ideas about what language, if any, would be OK?
 
[Begin quote]
 
Folks:

This semester we had an incident in which a guest lecturer made racist
remarks during a class.   The incident caused a great deal of hurt and
anger in the students who are acquainted with it.  I have met with a
number of students to discuss the incident and what to do concerning
it.  While the responsible party was not a member of the faculty or even
an appointed lecturer, she stood in the position of an instructor when
she made the remarks.  The Lecturer in charge of the class did not take
steps to address the matter and things grew worse.  In an attempt to
prevent a recurrence of such an event [the Dean] is working with
students to draft language that will  go into the handbook that we will
provide to Lecturers when we hire them to teach a course.  The language
will make our policy on this issue clear.  We will not tolerate an
instructor's use of racist, sexist or homophobic expressions in the
classroom.  Boalt has to be a place where all people feel themselves to
be a part of the community.  We will do our best to make everyone aware
of this fact in the fall.  I am sorry for the distress caused by what
happened this semester.

As to this year's incident, I will work with the Associate Dean to deal
with the personnel issues involved and we will resolve them once exam
period is completed. . . .
 
[End quote]
 
I should say that in my view this is far from an easy case for First Amendment protection for the lecturer's speech.  It seems to me that when people are hired by a law school to speak to law students, the law school should have the right to in considerable measure control their speech.  (I think that as a matter of sound academic freedom policy, instructors should have considerable freedom over their classes, but I doubt that the First Amendment imposes this as a constitutional mandate.)  On the other hand, I know that others disagree; and I know that some cases -- Cohen (9th Cir.) and Silva (D.N.H.) -- have struck down some policies controlling faculty speech on vagueness grounds (a serious problem, given how vague "racist," "sexist," and "homophobic" might be).
 
So I wonder what list members would think about this.  May a law school, for instance, prohibit faculty members or lecturers from ever stating their views that men's and women's brains and thus capacities are biologically different, and therefore that their legal rights (e.g., under the Equal Protection Clause) should be different?  May a law school prohibit faculty members from expressing the view that same-sex marriage should be prohibited because heterosexual couples tend to make better parents than homosexual couples -- or from inviting guest speakers who express this view?  May a law school prohibit faculty members from teaching a seminar on The Bell Curve, and expressing the view that the book's authors were probably factually correct about racial differences in intelligence?  Which, if any, of these would be prohibited under a policy banning "racist, sexist, or homophobic expressions in the classroom"?
 
(Incidentally, if anyone has the details on the incident that prompted this, I'd love to hear them, though I think the policy's validity or invalidity is unaffected by such an incident.)
 
Eugene