The prefatory clause of the 2nd amendment does not require a well-regulated militia to be in existence in order for the right to be protected, it expresses the motivation and then declares the right uninfringeable:

"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

Maybe you'd be happier if it said:

"The right of the people to keep and bear Arms while they are members of a well-regulated militia shall not be infringed."

I am sympathetic to both sides of the jurispredential pragmatism/literalism question, but don't get your eggs twisted about what the 2nd amendment says, as only the most alien of consciousnesses could find ambiguity in its terse declaration.