In the aftermath of the Aurora, Colorado shooting, there have been many commentators who posit that there is no reason for anyone to be able to purchase an assault weapon such as that which was used in the shooting.
In order to answer this question we have to ask ourselves, "What did the Framers intend when they included the Second Amendment in the Bill of Rights?"
First of all, the Framers were men who had lived through (and in many cases fought in) perhaps the most unlikely and auspicious victory in the history of wars -- the victory of agrarian colonists against the mighty British Empire. This David vs. Goliath battle left the Framers with a clear respect for, and confidence in, the power of a determined and armed populace as a bulwark against tyranny and abuse of power.
Secondly, the Framers recognized that the risk of tyranny did not necessarily have to come from a throne an ocean away, but could just as easily arise from within and so the citizens should be equipped with the resources needed to wage war against their own government if needed, just as they had against the British.
In other words, the Second Amendment is a license to armed insurrection since the threat of armed insurrection may be the only realistic obstacle preventing a leader from becoming a tyrant.
Under current law the rights of the citizenry to keep armaments is severely restricted. For example, average citizens cannot own fully automatic weapons such as machine guns, nor can they own grenades or rocket-propelled weapons, all of which are readily available to the military. So, does the implied "license to armed insurrection", subject to existing restrictions, still serve as a deterrent to tyrants, who control the military and ostensibly can used it as they fancy?
I think the answer is "yes" and "no". Clearly, no small group of rebels could ever hope to wage open war against the U.S. Army, and to that extent the answer must be "no". But, if the intent of these rebels is to martyr themselves to the cause of freedom and thereby inspire a wider rebellion, then even the greatly curtailed Second Amendment that we have today is a deterrent in that even the U.S. Army could not put down an insurrection by the majority of the citizens armed with the armaments that they are currently legally permitted to own. Whether the martyrdom of a small band of rebels waging war against tyranny would be sufficient to rally to arms the masses of people is doubtful, so I think that the answer to this open question is probably "no".
Therefore, it is clear to me that the Framers intended for the citizens to have at their disposal weaponry sufficient to oppose tyranny with a threat level that might give a tyrant pause, and so the citizenry must be entrusted to arm themselves with weapons that rival those of the regular army if we are to sufficiently respect the intent and purpose of the Second Amendment.
