An interesting and much-needed analysis, thank you!
I would add a couple of points, though — well, what you’d expect from a philosopher…
When people quote Mill in support of the jerks who want to scream their rubbish in my ears claiming it is a valid instance of of freedom of speech, I find it amusing. Mill, being a rather acute person, noted in his much celebrated “On Liberty”:
“An opinion that corn-dealers are starvers of the poor, or that private property is robbery, ought to be unmolested when simply circulated through the press, but may justly incur punishment when delivered orally to an excited mob assembled before the house of a corn-dealer, or when handed about among the same mob in the form of a placard.”
Rightfully so: in his framework, the raison d’etre for freedom is its utility, i.e., bringing more and better ideas to the market of the minds (seriously problematic, but let’s stick to Mill). Shouting “Kill the Muslims!” to a hyped-up crowd is a radically different type of speech act. Moreover: shouting “Drink more milk!” in a concert hall is no expression of the freedom of speech either — it is simply irrelevant and just annoys those who gathered to listen to Bach, thus restricting their freedom. This leads us to the second, most important point.
Universities are not open to all speech. And they should not be. They are churches of reason, as Pirsig so perceptively suggested. Universities value opinions that are supported by arguments. Arguments that are at least formulated in a way that has a potential to support their validity. A person who claims that 2 minus the square root of -6 equals Homer Simpson has a place in a lecture hall only if she can bring up an argument, logical or empirical, in support of her rather unusual claim. This applies across the board, from mathematical logic to astrophysics. University is not just any Agora — it is the Agora of reason. It serves the enhancement of human knowledge, not as a platform for expressing any view. Just like a library is no place for breeding rare slugs or repairing motorcycles.
Thus, I see two reasons to bring a speaker to school. The main reason would be that the claims the speaker makes merit serious consideration: they are supported by reasoned arguments. New theories in physics or philosophy can be a good example. The second case is when certain claims are hard to come by yet there is value in introducing students to them. For example, as Christ notes, they will make students to know the world better. Eco-anarchists’ opinions are hard to come by, so it might make sense to bring one on campus to speak. On the other hand, standard liberal views are quite well-known and accessible, so bringing somebody who will real Mill’s “On Liberty” aloud and cheer would make little sense: it is studied in virtually every Intro to Philosophy course and is present in any library, physical and online.
Do Milo Yiannopoulos, Ben Shapiro, etc. answer any of these criteria? Their claims are rubbish, if we are to use a polite term. And they are really not hard to come by. In fact, in the current media environment, they are hard to avoid. Moreover: if we are back to Mill, in the current climate some of them might well be akin to to an opinion that the poor are murderers of corn dealers delivered to an excited neo-Nazi mob Christ wants to welcome on campus.