> would you argue that the definition of a "well-regulated militia" has changed in the last 240 years
That's a good question. And the answer is yes.
At the time it was written, that phrase would roughly mean well-organized, well-armed, well-disciplined. Not regulated in the way we use the term today, to refer to something governed by regulations.
the whole point of the people bearing arms, is to enable the people to regulate the activities of a militia directed by a tyrant, example being rebellion against the occupying redcoats, the commision of the war of independance, and succesion of the republic.
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.
SCOTUS certainly hasn't interpreted it "as written", but has been happy to "evolve" it.