Since you're apparently an expert in the colloquial interpretation of 18th century American English, could you please explain what this part of the 2nd amendment means?
You're looking at the language and purpose of the amendment incorrectly. To translate its essence into more modern parlance, if would go something like: "Because it's always going to be necessary to have a trained and equipped military organization ready to defend the country, the government - in the interests of not allowing the government to have a monopoly on the tools of defense - shall not prevent citizens who are not in the military from having arms."
The people who wrote that amendment still had a very bad taste in their mouths from living under a monarchy that DID reserve the power to capriciously allow only the military to keep and bear arms. Knowing that a military/militia is necessary, they used the second amendment to be VERY clear that they considered the fundamental right to keep and bear arms to be NOT exclusive to the military. Just like the considered the freedom to speak to be not under the control of the government.