The weapon aspect they are afraid of is the act of premeditated assault. Which is legitimate. It would serve more like a shiv. With that said so can a tooth brush, pencil, and a chipped piece of concrete. But which one easier to outlaw to help you sleep at night. Knives are tools but are also inherently dangerous. Just like chainsaws, hammers and axes. Education and practice keeps them safe and effective. The school was clearly missing the point. But so are some of your viewers.