I just read the first part of this thread and a point about the North Hollywood robbery grabbed my attention; the fact that the police had to acquire arms from a nearby "gun shop" to match the robbers. Doesn't that impact on not the second amendment, but rather, the third, in the event that the owner refused to sell/let the police enter into his (granted although that they are commercial) premises?
Also, the right to bear arms is based on the principle of forming a milita against a hypothetically tyrannical central government. How does arming everyone against everyone else apply? As soon as someone goes on a rampage, does that somehow suddenly make them an agent of "federal oppression"? Isn't the colloquial argument that if the principal or security had a gun, it would prevent or significantly reduce the toll of a school massacre, also counter-intutitive to a general freedom to possess guns? It's a person of authority entrusted with general protection, but, as Shifty pointed out, they can just as easily turn the gun on a massed huddle of civilians too.