Personally, I think we should arm teachers. Annual background checks, monthly appointments with therapists to ensure mental well-being, the gun must be concealed. Stuff like that, to keep it out of mind, but there in case of emergency.
We can't carry automatic weapons around. Ownership of them is already tightly regulated. In fact, I don't believe it's legal to carry around a semi-auto rifle in most places.
What we're capable of owning are civilized variants of weapons, such as the PS90, a civilian P90. (Not trying to start a fight, just informing)