you keep ignoring the concept of "Well Regulated".
Lanza walking into a preschool with a bunch of weapons is not "Well-regulated."
back when the 2nd Amendment was written, "well-regulated" meant "maintaining competency by means of regular target practice"...
and if you bothered to read what the framers intended (and they left behind a plethora of writings on the subject), you'd know that the 2nd Amendment was indeed about an individual's ability to keep guns...
Back when the 2nd amendment was written, the most firepower an individual could garner was a Flintlock Musket.
According to the Continental army training manual, there were 13 steps to firing a musket. In short, a soldier had to get a cartridge, tear it open with his teeth, put a little bit of powder in the firing mechanism, put the rest of the powder and a gun ball down the barrel, ram the ball and powder home, cock the musket and fire.
The musket was not an accurate weapon, so even after all that work, the soldier didnt have the greatest chance of shooting his intended target. ref.
Which is why rifles had Bayonets on them. After you failed to hit your target, you just stuck him with the bayonet.
Oh, wait, don't bring up bayonets... it's likely to put LadyShitSlinger into a tizzy.