Political rights and freedoms are only secured through the exercise of power. Inherent in these rights is the necessity of defending said gained rights. What it really comes down to is whether or not you trust your government.
The United States Constitution exhibits implicit distrust in the State. The group of men known as the 'Founding Fathers' were of the opinion that regardless of the character of a man when he enters politics, he will invariably be corrupted to a degree. Thus, the USA have a checks-and-balances system, wherein the three branches of the federal government have limited decision-making powers and limited veto powers over the other two branches.
They went beyond self-regulation, however, and included the ultimate fail-safe into the very wording of the Constitution. While people who are in political unrest will revolt as they see fit, the USA has the only national government where you have a right to rebel explicitly stated;
"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness. That to secure these rights, governments are instituted among men, deriving their just powers from the consent of the governed.
That whenever any form of government becomes destructive to these ends, it is the right of the people to alter or to abolish it, and to institute new government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their safety and happiness."
The Declaration of Independence was written by British citizens in America who were well aware of the UK monarchy's history of controlling power among its citizens by the confiscation of weapons.
“Weapons are the tools of power. In the hands of the state, they can be the tools of decency or the tools of oppression, depending on the righteousness of that state. In the hands of criminals, they are the tools of evil. In the hands of the free and decent citizen, they should be the tools of liberty. Weapons compound man’s power to achieve whatever purpose he may have. They amplify the capabilities of both the good man and the bad, and to exactly the same degree, having no will of their own. Thus, we must regard them as servants, not masters – and good servants of good men. Without them, man is diminished, and his opportunities to fulfill his destiny are lessened. An unarmed man can only flee from evil, and evil is not overcome by fleeing from it.” Col. Jeff Cooper
But, more important than any of this --- it is far more likely you will shoot your foot, shoot your wife, shoot your neighbor's dog, or have your child shoot herself, than it is you will encounter a mass murderer.
While I would whole-heartedly agree that proper training (free training, since it is a Constitutional right) should be requisite of firearms ownership to avoid the kind of situations you described, your logic that a political freedom is less valuable because it can be misapplied is not universal.
Should we ban free speech because people commit slander and libel? Should we ban freedom of the press because of trashy and destructive tabloid magazines? Should we ban freedom of religion because there are kooky brainwash cults? Should we ban freedom of assembly because of hate-group gatherings?
The vast majority of firearms owners are mature, responsible, civic-minded individuals who obey the law and respect the rights of their neighbors. An armed society is a polite society.
For proof, just look at how gun crime has sky-rocketed in Britain
after they banned handguns. The only victims of gun control are the people who need to defend themselves.