A well regulated militia, being necessary to the security of a free state, the right of the people to keep in bear arms, shall not be infringed.
I believe that the Second Amendment was written in keeping with themes of Federalism. Federal Courts, Congress, and the President each constantly struggle for more power, the individual struggle of each being perpetually blocked by the struggles of the other two branches. The endeavors of the Senate (appointed by the State Legislatures) being countermanded by the undertakings of a House of Representatives elected by the people. Outside of the struggles of the Legislature with itself, and of the Federal Government with itself, the Federal Government jockeys with the States for power, the States themselves, if well-developed, having similar systems.
In sum, every governmental official fighting every other governmental official/body for power, each offering the others a check on that battle. All the men who desire great power and go into politics having their aims frustrated by all the other men. Furthermore, each man wanting to be elected, he must compete with other men in the hearts of the populace. In this free market of ideas, competion will allow the buyer (voters) to properly maintain their freedom.
It is in this very vein I feel the Second Amendment fits. An armed populace is a check on governmental power. Had the adults of the 12 million people Hitler killed all been armed, Germany simply could not have murdered them all, having only only 16 million people serving in the army between 1939 to 1945. Mao Tse Tung, in his Little Red Book, once said "Political Power grows out of the barrel of a gun". I think he was right, and I believe the founders wanted the people to have this trump card, should any small cadre of government officials get out of order.
It is from this point on, having offered my preamble which I believe serves as my own guide for answering this question, that I ask you: when it comes to the Second Amendment and the arms it protects, what types of weapons do you believe are inclusive to arms, and what not? Men should be able to have only blackpowder rifles? Or only modern hunting weapons? Pistols too? "Black rifles"/assault weapons? Full automatic weapons? Artillery? Chemical gas? Nuclear weapons? Biological weapons?
At some point there, I think most of us draw the line. Where do you draw yours? What do you think should be allowed to man? To engage the extremes, I believe blackpowder rifles serve no check on the power of the Government's weapons, while biological and nuclear weapons give the individual crazy too much power. (Noting that there is no doubt if he was not blocked by Federal Power, a man like Bill Gates could buy an atomic weapon from North Korea, as even boy scouts (reprinted) and college students (last 3 paragraphs) can and have make/made breeder reactors.) Indeed, as an addendum, let me simply say that whether or not the framers believed originally that all weapons should be allowed to be borne, the advent of nuclear and biological weapons offered a paradigm shift the likes of which they could not have dreamed. "Civilization crushers". With that in mind, I note that the Constitution is not a suicide pact, and even if the framers did not mean to exclude any type of weapon, whether or not you believe we should, on your own bases for why you believe we have the Second Amendment.