Putting hte 2nd Amendment into context: it was both a justification for what they had done in the Revolutionary war (in line with many of the philosophers at the time) as well as a justification for them to rebel again, if necessary. Back then, there *was* no difference between a militia formed of otherwise civilian members and the army. The 2nd Amendment was *not* put in place to allow hunters or shooting range officianados. It was there specifically to permit the government from being capable of controlling citizens because the citizens would be unarmed and therefore less able to resist government oppression.
It's much easier to understand the Constitution when you realize that it was primarily a boundary defining document when it was conceived. Basically the main document was there to say "these are things teh government could do." Many Federalists were against an explicit BIll of Rights because they assumed that because the Constitution didn't specifically grant the government power to restrict those rights, it was unnecessary to specifically grant them. This group was afraid that delimiting the rights citizens would have would make the people think that these were the *only* rights given to the people. Whereas those who objected to the Constitution without a Bill of Rights were afraid that because no rights were specified, it would be interpreted that none were granted. Thus, as conceived, the main body of the Constitution was conceived to specify what the government could do, and then not go any further, and the Bill of Rights was added to say "and they DEFINITELY can't go here."
Looking at historical Constitutional treatment, it appears that anti-Bill of Right Federalists were correct in their fears: Today we treat any right not specifically granted in the Constitution as fair game for removal by the government.
I'm not trying to take a side with the above spiel, but I'm sure some came out. So let me specify:
I believe that the militia and the right to bear arms does not specifically refer to an institutionalized armed force controlled by the state or federal governmnet. It doesn't make sense, since why wouldn't a government have a right to make an army? Plus that ability *is* specifically stated in the main body of the Constitution when it gives power to make war. Thus the second amendment must be granting permission to groups other than the US Army/National Guard/etc
I don't believe the Bill of Rights was a mistake. While those who opposed it were right to fear that we would have rights restricted, I don't thyink the presence of the Bill of Rights is solely responsible for that attitude.