trogdolyte, you raise an interesting legal point:If I am willing to stand in harm's way to protect them, why can't I have the tools I need?
It is long settled that the police have no duty to protect you or your students. By depriving you of tools of defense or restricting their availability and application, The State has created what is known legally as an impossible condition. You are entitled to default on any obligation of a contract governing that particular aspect with no penalty in such circumstances. Seems like this is legal justification for the possession of any self defense mechanism, although it has not been tested to my recollection.
A classic case of the impossible condition occurred not to long ago where a young woman, previously denied a concealed carry permit, was later raped while defenseless after calling the cops during the incident. I cannot recall the case particulars.
Of course, it is a vested interest of government officials to prevent a breaking of the social contract. They could all lose their retirement benefits, and have to get real jobs like the rest of us.