The private ownership of weapons is based on the philosophical principle of the basic right to self-defense, which the Constitution simply reflects and recognizes, much as it does with other natural rights. "Interpreting" the "living Constitution" to imply that individuals have no right to be armed makes no difference in the basic principles. While governments are instituted to place the right of self defence under the rule of objective law, that does not invalidate the original rights, but supplements them.

As for what the Founding Fathers thought, I (yet again) offer these quotes, which plainly show their support of an armed citizenry as a bulwark against tyranny. Judging from the quotes, they sure as hell thought most Americans had, or should have, guns. Again, note what I have pointed out before: the distrust of the Founding Fathers for a standing, permanent Army.

The use of interchangable parts to manufacture guns began in the very late 1700s. Until then, it is entirely likely that a good gun was a luxury item, and hard to come by.

And, even assuming the data in that book was not "cooked," just because a lot of people did not own a gun is completely irrelevant in the argument from basic principles over the right to bear arms. Most people did not (and don't now) publish newspapers either, but that does not invalidate the concept of a free press.

I think if you look throughout history, people went around armed more often than not, especially in the upper classes. Peasants, slaves, peons, and other human property of their lords often went unarmed, but that was because they were forbidden such things precisely because of the threat of an armed citizenry against tyranny.