The link below makes some interesting reading. The poll was conducted by the CATO institute in collaboration with Yougov and surveyed 2,300 people.
America's Many Divides Over Free Speech
Rather than copy the whole thing, I'll include this section so you get a flavour of what came up:
When asked, “Suppose the following people were invited to speak at your college, should they be allowed to speak?” respondents who were college students or had college experience answered “no,” various viewpoints should not be allowed, as follows:
- A speaker who advocates for violent protests (81 percent)
- A speaker who plans to publicly reveal the names of illegal immigrants attending the college (65 percent)
- A speaker who says the Holocaust did not occur (57 percent)
- A speaker who says all white people are racist (51 percent)
- A speaker who says Muslims shouldn’t be allowed to come to the U.S. (50 percent)
- A speaker who advocates conversion therapy for gays and lesbians (50 percent)
- A speaker who says transgender people have a mental disorder (50 percent)
- A speaker who publicly criticizes and disrespects the police (49 percent)
- A speaker who says that all Christians are backwards and brainwashed (49 percent)
- A speaker who says the average IQ of whites and Asians is higher than African Americans and Hispanics (48 percent)
- A speaker who says the police are justified in stopping African Americans at higher rates than other groups (48 percent)
- A person who says all illegal immigrants should be deported (41 percent)
- A speaker who says men on average are better at math than women (40 percent)
Do you think any of the above viewpoints should not be allowed? Is free speech too restricted now or does it need greater restrictions?
Considering that this is in the context of a speech at a college or university, then it's not strictly a "free speech" issue in terms of what kind of speech is acceptable. In general, I tend to agree with the basic principle behind the "clear and present danger" rule. Even discussions about violently overthrowing the government would be allowed, as long as it remains abstract and hypothetical, not someone openly calling for and enjoining others to violence.
At a college, I'm not really sure. It's been a while since my college days, so I'm not clear on how much they can allow or disallow. If a tenured professor employed by the university said any of these things, then there may be a matter of academic freedom where they might have to allow it even if it's offensive to some people. If it's just an outside speaker who's only visiting, then they might have more discretionary power.
Of course, on the matter of academic freedom, one might well wonder why a university or some other institution of higher learning would even have to consider the question of what they should "allow" or "not allow." Is it no longer possible to have an open discussion about a controversial topic without people going off screaming like a bunch of wild banshees?