For something that was supposedly intended to be easily understood by the people we certainly have a lot of confusion and argument.
To address one argument concerning the interpretation of "invasion" versus "terrorist attack," we might consider that technology over that past few centuries has changed most concepts the founding fathers held. Back in the days of muzzleloading flintlock rifles and pistols, about the only difference between the military and the people would have been uniforms and cannons. An invasion in those days would have been a military maneuver and that concept has changed drastically in recent decades.
Today, we are not looking at a handful of yahoos trying to overthrow the government with deer rifles. We're talking about an individual freedom to defend ourselves one-on-one against a domestic violator. Such freedom was probably simply taken for granted back then, as it should be today.
I'm guessing that if the founding fathers had even a clue what things would be like today, the Bill of Rights may well have been enough to fill a library. In any form of government there will be those who thrive on power and control. In many ways, a democracy can end up much like a dictatorship with no single ruler.
If we don't have individual rights, we have none at all.