The right to self defence is inharent, as noted by the "right to life...." in our most famous founding documents.
This right does not end when someone clocks in at their job, and most certainly does not end when a citizen steps foot into a state ran office.
This action is illegal at its base, and even worse it is meaningless as anyone wishing to do evil will continue to do evil. This will only strip the rights away from law abiding citizens.