This comes down to respect. A good teacher thinks about and validates students' contributions to debate. This puts professors in difficult positions. Every classroom has certain norms of discourse. For instance, professors are no longer free to make comments about women's breasts.
Some speech has no cognitive value.
It doesn't advance discussion. I would to see a norm against speech that silences others. My freedom to articulate my point of view doesn't free me from others' criticism. It could be based on hatred and used as personal invective. Research programs may be accused of being racist because attention is not paid to certain points of view.