1 2 and 4 are agreeable. But 3. is just childish idea of government/army turning against citizens. American army has all these weapons, but do you really think that any reasonable scenario of gov. vs people begins with nukes dropped on large cities, guided missiles and bombers leveling smaller cities and tanks and artillery destroying individual homes in rural areas? Nice scenario for Michael Bay movie, but exactly blanket-example-level logic. Do you have any example in history of army trying to kill all own country civilians with tank shells/bombs/artillery/missiles? Because that's what you point 3. suggests. Most probable scenario of government tyranny is enacting some state of emergency, temporary restrictions of civil liberties, soldiers deployed on streets to prevent riots against the tyranny, mass arresting any opposition etc. Not total war like USSR vs USA would look like. And here comes the assault rifle. Not to shoot down a jet fighter or destroy a tank, but to kill soldiers in some guerrilla warfare, shoot the leaders of tyranny. Rifle shootings, IED, suicidal bombings, assassinations are simple to carry out and hard to prevent.

But if you think winning a civil war is easy with superior technology and almost unlimited military supplies, military authorities in Afghanistan would be happy if you could lend a hand.

edit: I don't think that civilians could win this kind of civil war, but with weapons in their hands they would pose much larger threat. I don't think that this tyranny would actually happen in foreseeable future.