Militias come baked into the Second Amendment. The concept is that militias are necessary for the defense of a free state - and the defense of the people from the state. Bear in mind that the US Constitution was written two hundred years ago and the US didn't even have a standing army, and the Second Amendment's primary purpose was to prevent the need for one.

This has led to a cultural belief within the US that the government's fear of its own armed populace is the only thing keeping it from degenerating into tyranny, and the establishment of the "militia patriot" as something of a romantic folk hero like the cowboys of the Wild West.