Calling the cops can be appropriate, depending on how over the line the kid was. Considering the police took him away, Id bet he was not simply disputing the schools right to require him to change his shirt.
If the shirt violates policy, then he was in the wrong. If not, the school is in the wrong. As to the arrest, that is a police matter and has nothing to do with the school.
It's appropriate when the goal is to enforce the concept of a police state. That certain ideas, such as supporting the United States Constitution, will be met with arrest and imprisonment.
Such is the case in this story. The teachers and administrators wanted to send a clear message that support of the old Republic and that Constitution, written by "dead white men" would bring severe punishment.
You analysis belongs on a pig farm, Uncensored, with your nonsense talk of totalitarianism. You are one of the most authoritarian figures on USMB.
When a child is confrontational and elevates an argument, the teacher must elevate the response level to make sure all personnel at the school, including the student, are safe.
Calling the police was exactly the right thing to do.