No form of dishonesty is acceptable. I will promptly and publicly fail and humiliate anyone caught lying, cheating, or stealing. That includes academic dishonesty, copyright violations, software piracy, or any other form of dishonesty.
When he found six students plagiarizing on an assignment, he followed through. The university fired him. I'm with those who say that, as a matter of university policy, it was obviously right for them to do so (but see below, because it is not merely a matter of university policy); it was a pretty clear violation of FERPA regulations as they are usually understood, particularly without a hearing being called, and universities simply cannot overlook something like that, however unfortunate the results. (Even setting FERPA aside, it is a violation of professional academic ethics. Public humiliation is not something that can be called back. If you give a student a zero for cheating, the student has means of appeal, and can make a case for guaranteeing that the zero does not appear on the record, no harm to the student. But if you humiliate a student in public, you are giving a punishment that cannot be undone before a student has the means to see that his or her case has been reviewed and rights protected. You could later apologize, but that's not undoing the punishment. In any case (not that I'd expect most people to be moved by the point), things like this also come dangerously near the sin of detraction. Deliberately damaging someone's good name, even for something you are fairly sure is true, is not a minor matter; it is one of the most serious punishments you can inflict on an individual. It is a massive harm in itself, and its effects are extremely difficult to predict; and it should be treated accordingly, like the dangerous weapon it is. And this is particularly important for people in academia, since in our hands it can be even more dangerous. Not every case of public humiliation is detraction, but there must be safeguards in place to prevent it from becoming so. There are reasons that students are protected from this.)
But I don't actually blame the adjunct professor here. Just from what I've read about and by him, he seems like someone who was genuinely trying to build the best course he could. It's important to note that he had never taught before and is not a professional academic: he was a qualified professional asked by the department to teach a course in his area of expertise, and who agreed because he thought it an opportunity to give back to the community. His syllabus was reviewed by the department chair, who did not catch the ethical risk in the provision. Befor posting the grades, he gave the university forewarning and was not corrected. It's unfortunate that someone who, to all appearances, had an enthusiasm for the course and a genuine interest in giving his students the best course he could was put in this position. I hope that this doesn't discourage him from continuing to take an interest in education, since we could use more of him; I don't think there was anything else the university could have done, but he seems to have been put in a very unfortunate and ethically risky situation through no fault of his own. You can get his side of the story here, and his argument that plagiarism should be brought out into the open in the same place.
Actually, I'm not convinced that even academics are given what they need to fulfill their professional ethical responsibilities. Before anyone is allowed near a classroom, they should be made to sit in a class and learn, quite clearly, all principles governing the professional ethical issues that are involved in being a modern instructor: ADA, sexual harrassment, FERPA, student rights, academic rights, university policies, &c. A lot of schools get part of this in already with their professional development requirements; but doing it that way guarantees that it is piecemeal.