Nevertheless, I assume the teacher was responding less to the challenge and more to the mode of challenge. That's a matter of taste, to some degree: academia is supposed to be able to sustain robust but civil disagreements, but what constitutes the boundaries of "civil" are very much under contest. The excerpts from the professor's letter suggest that other students were highly uncomfortable, and that he had issued multiple warnings before the ban. Online student-reported feedback suggests that he's a good professor: he rates near the top in all categories except "easiness," where he rates at the bottom. This is exactly as it should be. I'm inclined to trust his sense of his environment.
Besides, it sounds as if the professor's claim that there were sexual assault survivors in the classroom is extremely plausible:
Despite its small size, Reed’s students reported the most sex crimes of all colleges and universities in the state of Oregon during 2010–2012 and ranked third in the number of reported assaults per 1,000 students in the country in 2012.Sounds like part of the reason the student's mouth was such an issue is a complete failure of the college to uphold other standards. That's neither the student's nor the professor's fault, but it can't help but be a factor here. Reed as an institution bears the real shame in this story.