Two more things:
First, that the people who commit murders with guns are a minority of the gun-owning population of any nation that allows civilian gun ownership. Like anything else, it's a few whackos giving the rest a bad name.
Second, that no one today really knows how to set up a "well-regulated" militia for the purpose of overthrowing an oppressive government in today's age of modern warfare. Here's how I think it might work:
1. [Prerequisite] Own a large corporation with the power (money) to build/buy aircraft, heavy weaponry, private fortresses/airstrips, and all the other trappings of modern warfare.
2. Start building/buying all that stuff.
3a. Require compulsory "security training" for all able employees, but offer incentives such as free housing or tax-free income (we're overthrowing the government, so there's no need to pay taxes).
3b. Use propaganda to brainwash all employees and their families.
4. If government tries to stop you, fight back (i.e. let them strike first).
5. Surprise attack Washington, bombing capitol building, White House (or wherever the Prez is), and Pentagon (taking out NORAD (if possible) might also be a good idea)
6. Now that the federal government has been attacked from within the nation, chaos will ensue and the states will eventually try to form their own governments to deal with the chaos of revolution. Therefore...
7. [Optional] Unify the states under a new government.
A few anti-government zealots aren't going to overthrow anything. In order to overthrow an oppressive government, a group must (temporarily) have near total control over a lot of money and a lot of people, but must then be willing to give up that control once the oppressive government is overthrown in order to prevent becoming just another oppressive government. Unfortunately, human nature doesn't work that way; people in power will always try to stay in power. No corporation is ever going to gain control over a lot of people, overthrow one government, set up a new government, and then just release control over those people.