"With me everything turns into mathematics."
"It is not enough to have a good mind. The main thing is to use it well."
"It is truth very certain that, when it is not in one's power to determine what is true, we ought to follow what is more probable." -- Rene Descartes
Another way of looking at it is to say that the students really don't have any "rights" at all when it comes to this kind of school sponsored event, since the school really doesn't HAVE to have a graduation ceremony at all. It's all done FOR the kids.
Ban? I would support the school's decision to implement that rule, definitely. Flipping out if the kid ignore said rule? That's a bit silly. The Valedictorian decided to show how little respect he has for his fellow students and faculty by giving them the proverbial finger, so what? A lot of people are a-holes in this world.