By the time the 2nd Amendment came about, we already had an army called the Continental Army. It was comprised of volunteers.The 2nd Continental Congress formed the militia at the state level, comparable to today's National Guard.
I'm curious as to where you are getting your history from. The Continental Army was disbanded years before there the Bill of Rights was ratified. The Militia's existence preceded both the 2nd Continental Congress and the Continential Army.
Anyway, it shouldn't matter to you what the 2nd Amendment says or what the founders intended. As a liberal, aren't you one of those "living constitution" guys who think the Constitution should be reinterpeted to reflect the whims of the day?