“A well regulated Militia, being essential to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.” U.S. Constitution, Amendment II 
That’s the Second Amendment, one of ten included in James Madison’s proposed first thirteen amendments to the Constitution. Ten of those thirteen were fairly promptly ratified and became the “Bill of Rights”. They are rightfully thought of as a bulwark against the over-expansion of the strong central government that Hamilton had pushed for, and specifically protections for the individual against the power of the federal government (and, since the ratification of the 14th Amendment, against the power of state and local governments).
The U.S. Supreme Court’s current conservative majority has taken the Second Amendment in this context, and has focused on its second half, “…the right of the people to keep and bear Arms, shall not be infringed.” In doing so, however, that majority has violated a central canon of statutory construction – that a statute (or constitutional provision) be interpreted to give meaning to every word of the statute.
The first half of the Second Amendment, “A well regulated Militia, being essential to the security of a free State,” can be seen as a preamble, or perhaps more precisely as a context for the second half. Another rule of statutory construction is that the words of a statute should not be read in isolation, but in context. Here, the context of the second half of the amendment is protecting “a well regulated militia” and its function of protecting “the security of a free State.”
In other words, the right to keep and bear arms is protected so that the people of the United States can continue to have “a well regulated militia”. Again, keeping the context in mind, in 1789 (or 1791) there was no standing federal army. An army was raised as the need arose. In the meantime, there were local and state militias – what we would now call paramilitary organizations, or perhaps militias as the term is used in places like Afghanistan and Iraq.
So, in that context, the right of “the people” to keep and bear arms is not an individual right, but a right of the people as organized into militias. Further, those militias were intended to be, “well organized”. Indeed, that was supposed to be the central purpose of having the right to keep and bear arms. A militia needs training and discipline if it was going to function well to protect the security of a free State. (And again, this should be taken in the context of a document written ten years after a prolonged war against what was then the central government, and fought largely by local and state militias organized under General George Washington.)
Bringing those concepts into the 21st Century, the right to keep and bear arms does not protect an individual’s right to own and carry guns (or sabers, or hand grenades). Rather, it protect the right of the people, organized into well regulated groups intended to protect the security of a free State.
What do such organized militias include? Well, obviously they include the National Guard, as state militias have come to be known, and their members. They also include state and local police forces, which are intended to “protect the security of a free State.” They could also include well regulated local, state or national groups organized to protect the security of a free State. Could that include so-called “self defense” groups? Maybe. Right-wing paramilitary groups? Questionable. Groups of gun-toting skinheads or neonazis? Probably not. The Ku Klux Klan? I don’t think so. They certainly don’t include individual citizens who aren’t part of a “well organized militia”, and certainly not the millions of deranged individuals and criminals who now, thanks to the majority of the U.S. Supreme Court, claim the right to keep and bear [and use?] arms.
Those on the Supreme Court (and I am thinking specifically of Justice Scalia) who strongly espouse strict constructionism and original intent in interpreting the Constitution, appear to have been lured by ideological predilections into straying from their self-chosen narrow path by broadening the meaning of the Second Amendment. Perhaps, in the context of the Charleston Massacre, it’s finally time they reconsider.