To continue the point, I don't think the term "militia" is meant to be singular. It is a regulated body of people. In other words, I don't think that George Zimmerman protecting his neighborhood against Trayvon Martin would be considered a militia action.
A militia cannot be seen as a vigilante group. Multiple independent armed people are not a militia because they are not "well-regulated." As Madison states, they must gather periodically and practice. Practice means three things: 1) demonstrating that the arms are in proper working order, 2) demonstrating that the people are skilled in the proper operations of the arms, and 3) demonstrating that the people can act as an organized body during a call to action.
Individual policing would be hard to bring under the umbrella of a militia unless those people also participate in a regular militia order from time to time.
-PJ
It’s true that group organization is important for some threats. But modern times have changed the way militias are organized. Zimmerman on his neighborhood watch was very definitely militia activity because that is the way protection from neighborhood threats is organized. The people stepping up to the responsibility are few and far between, luckily we have enough Zimmermans to carry the load along with all of the liability as he found out.
The question of "who or what is the well-regulated Militia" is made less relevant by the fact that the Second Amendment does not say, "A well regulated Militia, being necessary to the security of a free State, the right of the MILITIA to keep and bear Arms, shall not be infringed.