One point about the wording of the Second Amendment that is often overlooked is the phrase "Free State." The usual assumption is that the Free State is the United States of America, in the modern Nation-State construction (a body of people with a common identity and the sovereign government that represents it). However, examination from the thoroughly jaundiced Anti-Federalist view does not bear that out. Any government will tend toward infrigement of natural rights, in the Anti-Federalist view; the only acceptable amount of government is the barest minimum to ensure the public good. Thus, by the Modern definition of State ("A political association with effective sovereignty over a geographical area", according to Wikipedia), a "free state" in the Anti-Fed view is simply a non sequitur.
Rather, what a "free State" must then mean is in modern parlance a free nation. A nation is a group of people with a common identity, which can (and do) exist without associated states. This fact is responsible for a significant chunk of global conflict; Kurdistan and Chechnya are the first ones that come to mind. The American Revolution would not have happened if this separate identity had not been created.
America has faced only one external enemy on its own soil - the British, in 1812. For obvious reasons, the need for a defensive standing army (as required in most of Europe) simply has not existed. An army needs an enemy to justify its existence, and the monumental resource drain it represents. With no external enemy, a standing army turns inwards, with historically predictable results. The Founders recognized this, which is why America had no peacetime standing army until after World War I. The Anti-Feds saw a standing army as an explicit threat to the freedom of the American Nation. Even then, the militia as a defensive body against external enemies is a secondary function.
The militia is the body of people capable of bearing arms, and thus synonymous with "The People." This was the prevailing definition at the time of the Constitutional Convention, and the one referenced by the Militia Act of 1903 (which created the National Guard). The National Guard, incidentally, is a federally controlled reserve military force. When deployed, the Guard functions as standard Army or Air Force units, answerable to the Federal command stucture (Joint Chiefs and the POTUS). To suggest that this is the same militia that requires the people to keep and bear arms is absurd, as it would convert the people's militia (when activated) into a tool of a government which, by nature, tends towards tyranny. This is recognized by the Posse Comitatus act of 1878.
This would lend credence to a States' rights reading, except that the States are a layer of government between the people and the federal government, as indicated by the Tenth Amendment. Furthermore, the States are still government, who exist to preserve the rights of the people (and provide for the public good). The State is a construct that exists because The People create it and allow it to exist; it is not The People.
The Second Amendment is thus the right of the people to organize against a government hostile to the people's natural rights. This right is any sort of free association up to overthrow, and the arms indicated are merely the tools that give the association teeth. If The People can keep and bear arms, it reaffirms that government exists by the good graces of its constituents. While self-defense is a natural right, defense of one's person from criminal actors is secondary in the context of the Second Amendment to defense of one's rights from a government. The former was recognized by English common law, and subsequently American law. (recognition of that right in certain jurisdictions is a bit spotty, but that's another rant.) The latter makes any restriction of the right to Keep and Bear Arms blatantly hypocritical, especially on the Federal level. These are the guys the second is supposed to reign in, and they're reigning in the second? One would assume an untoward vacuum in civics education at the Congressional level, or a wanton disregard for the Constitution. Neither possibility provides much reassurance.
Whatever percieved social benefits to firearms prohibition (at any level), the security of a free State - we, the American people - is an absolute requirement. The free State is threatened from without, but the threat from within is more insidious and potentially far more dangerous, and requires constant vigiliance...and the right tools.