But the problem is precisely that the quoted argument, if accepted, would push professors into silence on a wide range of topics. Certainly those would include any statements that may be perceived as conveying hostility to a racial group (and people would make that argument not just about overtly racist statements, but also about sharp criticisms of illegal immigration, of race-based affirmative action, of the Black Lives Matter movement, and so on).
They would also include any statements that condemn a religion, or religion generally, or irreligiousness generally. After all, if a professor argues that Islam is a force for ill in the world — or the same about Catholicism or Mormonism or what have you — that could make some people “worry he wouldn’t treat [Muslim/Catholic/Mormon] students fairly in his class.” And that’s true even if the argument is framed as calmly and rationally as possible. Indeed, if the professor just thoughtfully lays out the case for why Scientology is a scam, or Catholicism is supposedly oppressive, or all religion is irrational, a student who has publicly identified as Scientologist or Catholic or religious may well worry that this would translate into unfair treatment. (Wouldn’t it just be human nature for a person who has publicly condemned belief system X as irrational to think worse of people who believe in X, especially in evaluations where rationality is valued?)
But of course this isn’t limited to race, religion, sexual orientation, sex and the like, as the comment I quoted suggests — it would also apply to any political belief system. In this case, the argument is made that the person wouldn’t treat conservative students fairly. But students of all political stripes deserve fair treatment. (In public universities, discriminating against students simply because of their political beliefs, rather than class performance, would violate the First Amendment; in private universities, such as the University of Tampa, it would violate norms of academic ethics and may violate explicit university policies.)
If a professor harshly condemns Communism in a tweet or a blog post or a scholarly article or book, students might worry that he wouldn’t treat them fairly if he sees them wearing Che shirts or hears that they belong to pro-Communist groups. Likewise for Socialism, or environmentalism, or libertarianism, or any other belief system.
And, again, this wouldn’t be so just when the professor posts an offhand, mean-spirited slogan. A book that is the work of years of careful thought and argument, and that is sharply critical of some political beliefs could have precisely the same effect on students (and other observers) who are worried about the professor’s unfairly treating students who adhere to those beliefs.
So if professors can be fired because their posts show hostility to particular groups (political groups, religious groups, or otherwise), then we should candidly disavow any claims of academic freedom on the part of universities: Universities should acknowledge, to prospective teachers, to students, to donors, and to legislators that a vast range of opinions can lead to firing, and that therefore those opinions will be largely lost to debate at the university — and to public debate by university professors. Maybe that’s the university we want; but we need to decide whether we want it, and, if we don’t want it, we should reject the argument that professors should be fired for their speech on the theory that the speech shows that they “can’t be trusted to fairly grade” some group of students.
(I should note that, if one really cares about fair grading, one should at least institute anonymous grading, which I believe most law schools have. That would be an incomplete solution, because it wouldn’t prevent unfair grading of class assignments, such as term papers; and it would also prevent grading based on class participation. But I think that the loss of class participation grades would cause much less harm than would a policy of professors knowing that they can be fired for speech that will lead some to worry about their grading objectivity.)