Some words, like n****r, ch*nk, and c*nt, are so forbidden that we won't even spell them out here.
On The New York Times's philosophy blog, The Stone, Professor Ulrich Baer defends student protests of speakers with whom they disagree. Baer's core argument is that some voices in the public debate may end up excluding others from the public debate. This happens when someone's discourse dehumanizes certain groups in society. In these cases, Baer sees it as appropriate for students to protest in order to prevent these individuals from speaking. In fact, Baer sees this as maximally protecting our right to free speech, because those individuals who have been dehumanized can no longer participate in the public debate as equals.
I have a number of responses to Baer's proposal.
First, I think a version of this argument may end up backfiring. This would happen if we imagined our right to free speech as being "maximally honored" when we have the fewest number of voices being silenced. Suppose there are a group of bigots whose speech would dehumanize marginalized groups. If it turns out that the bigoted group is larger in number than the marginalized groups, then our right to free speech would apparently dictate to let the dehumanization continue. This suggests that we should either find a different conception of our right to free speech or find a competing value that trumps free speech in this context.
Second, I was skeptical of how often such student protesters are responding to speakers who actually dehumanize groups in the way described. Perhaps you can claim this about Richard Spencer, but it's a slightly harder case for Ann Coulter. Certainly Ann Coulter has made her share of degrading remarks, but you might think it's not that likely for her to show up to Berkeley and make such dehumanizing remarks.
Third, there's a difference between making dehumanizing comments and literally dehumanizing by way of your speech. There's an extensive debate amongst philosophers of language and political philosophers about this distinction, so I will merely gesture at it here.
Finally, I think Baer's suggestion may lead to certain political deficiencies in those trying to fight against oppression and marginalization. That is to say, if the left on college campuses want to be able to adequately counter the right's arguments in a larger public context, the left needs to learn the right's worldview inside-out. They need to understand why people buy the right's arguments, and listening to them speak is a good place to start.
Anyway, that's just my two cents. Here's the link to Baer's New York Times op-ed: