This concept of the people's self-regulation, that is, non-governmental regulation, is also in keeping with the limited grant of power to Congress "for calling forth" the militia for only certain, limited purposes, to "provide for" the militia only certain limited control and equipment, and the limited grant of power to the President regarding the militia, who only serves as Commander in Chief of that portion of the militia called into the actual service of the nation. The "well regula[tion]" of the militia set forth in the Second Amendment was apart from that control over the militia exercised by Congress and the President, which extended only to that part of the militia called into actual service of the Union. Thus, "well regula[tion]" referred to something else.
Since the fundamental purpose of the militia was to serve as a check upon a standing army, it would seem the words "well regulated" referred to the necessity that the armed citizens making up the militia(s) have the level of equipment and training necessary to be an effective and formidable check upon the national government's standing army.
This view is confirmed by Alexander Hamilton's observation, in The Federalist, No. 29, regarding the people's militias ability to be a match for a standing army: " . . . but if circumstances should at any time oblige the government to form an army of any magnitude, that army can never be formidable to the liberties of the people, while there is a large body of citizens, little if at all inferior to them in discipline and use of arms, who stand ready to defend their rights . . . ."
It is an absolute truism that law-abiding, armed citizens pose no threat to other law-abiding citizens. The Framers' writings show they also believed this. As we have seen, the Framers understood that "well regulated" militias, that is, armed citizens, ready to form militias that would be well trained, self-regulated and disciplined, would pose no threat to their fellow citizens, but would, indeed, help to "insure domestic Tranquility" and "provide for the common defence."