madaxe_again said that the University gave him a zero for plagiarizing a website when he was the one that controlled that website. Whether or not it is legitimate to post solutions online, this is not what madaxe claims to have been penalized for.
In my opinion, arbitrarily shoehorning a perceived infraction into a preexisting rule that it doesn't fit so that you can punish behavior that you hadn't thought to disallow before the fact is an abuse of university policies.
If madaxe is recounting the event accurately, then I think that the university is more in the wrong. University policies are hard enough to follow in situations like this when the university sticks to the letter of the policy. Plus, universities can always go back to update policies as they see new behaviors that they would like to disallow. But if the university uses whatever policies that they do have on the books to punish arbitrary behaviors that they don't disallow, then it puts the student in the situation of having to predict how this practice will impact them in the future. This is essentially impossible, and quite defeats the entire purpose of having policies written down in the first place. If this practice is common, then the policies are merely legitimacy theater, and are in fact illegitimate.
The situation is further confounded by the power dynamics at play. Tanking a students GPA is a pretty tremendous bludgeon, and outside of retaining a lawyer, a bludgeon against which students have little defense. This power discrepancy demands discretion on the part of the university. There is a level of injustice in the act of a university wielding this power against a student without a grounding in legitimate policy.