Well, first, we don’t know that they had “special permission.” It seems to me, regarding permission, that there are a few possibilities here.
One is that the student was lying, and they did not actually have permission at all. I doubt that this is the case, but i would still be interested to know from the university whether they had granted permission. If they did, i’d also be interested to know why, given the written policies.
If the students DID have permission, then it could simply be that, despite the written policies i’ve found, the university will generally grant student groups permission to chalk the sidewalks, as long as they ask first. That’s the practice on the campus of the CSU where i teach. To assert special treatment, you would have to show not only that the university granted permission, but that it had refused permission to other groups, and that its decisions were being made based on the content of the speech. We have nowhere near enough information to make this sort of claim.
And finally, even if the students did NOT have permission, you are absolutely incorrect about the role of the professor here. On a university campus like this, professors’ power over students is largely limited to their interactions with the students in classrooms and other areas where official university business is taking place. Those of us on the faculty have basically no authority over the general behavior of students on the campus.
In my classes, i can determine the syllabus, the workload, the assignments, the exams, and stuff like that. I can require students to undertake certain tasks, and i can require them to participate in certain activities, and i can even require them to be silent at certain times. If a student is disruptive to the learning environment and to the other students, i can require the student to leave the class, and call campus police if they don’t comply.
But outside my classroom, i can’t do jack. If a student drops a piece of litter on the ground, or parks in a faculty parking space, or ride a skateboard in defiance of campus rules, i have no special authority, as a faculty member, to stop them or punish them. I can, like any other person, tell them that they’re acting like a jackass or that they’re breaking the rules, and i can, like any other person, notify the appropriate authorities. But i don’t get to play cop just because i’m a faculty member.
If the students in this case were indeed breaking campus rules, what the professor should have done is inform them of this, and then, if they ignored him, he should have notified the appropriate campus authorities, which would most likely include the Plant Operations or the Facilities Management people, as well as the campus police. He could also have informed the Dean of Students, who is the person who often deals with disciplinary actions related to campus rules violations. And he definitely should NOT have encouraged his own students to confront the other students and start erasing their chalk. This sort of pitting students against one another is not something that we, as faculty members, are supposed to be doing.