Hre's the text of the 2nd Amendment:
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
You will notice (unless English is not your first language)that the first part of the sentence ("A well-regulated milita being necessary to the security of a free State...") condtions the second part ("the right of the people to keep and bear arms, shall not be infringed"). In other words, it was necessary for the population to be armed in 1789 because the government was incapable of defending or policing them.
Now, let's delve into a bit of history when discussing the 2nd Amendment;
When that was written, this country had just been founded. It had no constituted armed forces and nearly no constituted law enforcement organizations. It was a country which was weak, dangerously exposed to it's enemies (Indians to the west, European powers all along it's borders, potential counter-revolutionaries within it's midst). It's only natural defenses were the Atlantic ocean and the Allegheny mountains. It was certainly lacking in funds, and in some areas, authority.
It only made sense that "well-regulated militas" should be formed and maintained, given the lack of a regular army or law enforcement mechanisms. These shortcomings, however, were relatively quickly corrected with the formal,legal creations of such institutions. However, Congress never went back and made a further amendment to the basic amendment. The reasons for this are quite easy to explain.
What you enjoy NOW as "the right to keep and bear arms" is simply a custom, one which is in fact based upon Constitutional law, but, is a priveledge conditioned by the premise that to disarm an armed public (which in days of yore depended upon their weapons for a variety of reasons and had become accustomed to being armed), was beyond the scope of the government to do peacefully.
Viewed in that light, the proscription of certain firearms and the attachment of qualifications, licences, etc, to the owning of a firearm, is simply pragmatic government. If the government WANTED to take your guns, it would certainly do so (assuming our military and law enfgorcement folks who would carry out such a program were mind-numbed robots incapable of doing anything but execute orders, or devoid of independant thought), and your ability to own a flame-thrower or an anti-tank rocket would not stop them. You can disabuse yourself of the fallacy that you might be called upon to fight a second revolution as some sort of Minuteman against a tyrannic state, because the power arrayed against you is incomprehensible and certainly invincible if it ever came down to that. Your only hope in that case, would be that certain segments of the state would see things yor way and come to your defense (those military and law enforcement officials who decided for one reason or another that their orders were either illegal or immoral. This, incidentally, is almost a certainty, in my opinion, should that event ever come to pass. These are NOT automatons, but thinking individuals who prize their liberty just as much as you do).
Any other excuse to own a weapon (I like to shoot cans, I like the noise, I can defend my home, I have an uncontrollable urge to shoot inoffensive forest creatures to prove my manhood, etc) are Utilitarian in nature, and certainly not irrelevant, but not necessarily a reason to conveniently ignore the first part of the Second Amendment, nor nullify the right of legally-constituted government to regulate the use and owenership of weapons.
Whoops! Forgot to finish the point;
When we refer to bullet point 12, it is axiomatic of the fringe right that the United States government is evil and the greatest threat to liberty (or rather, what those people perceive as liberty) the world will ever know. There are those who actively and persistently advocate armed revolution against the United States government, vigiliantism, and terrorism on the far right (the Black Helicopter Gang). What many see as government doing it's job as instructed by it's citizens (the regulating firearms) these folks see as losing their ultimate means by which their lunatic fantasies will one day be enacted (armed insurrection).