The point of having weapons isn't in case we need overthrow the government. Hell, that wouldn't be a difficult task for hand full of motivated people. There are only some 540 odd people who control this country.
The public keeping weapons is to ensure the government doesn't see us a subjects. Without these weapons, what possible resistance would the government run into when instituting laws that eventually turn this country into a police state?
I'm not saying i believe that will happen, but it's not outside the realm of possibility. However, I'm sure that many societies never in a million years thought their government would make the decisions they did in the past. But their governments did, and millions have died for it.
"There is no greater tyranny than that which is perpetrated under the shield of the law and in the name of justice. -Charles de Secondat"