I do love all the attributions made by firearms enthusiasts as to the purposes of militias at the time immediately after the revolutionary war. They never were intended as a check against our own govt, at all.
The original 13 states had hostile natives all along their western borders, and still hostile & potent British forces in Canada. They didn't believe in a large standing army, either. Therefore, they sought to establish citizen militias, and to allow individual citizens offensive & defensive capabilities wrt those hostile natives & as a check against British Canada.
The issue of their own govt being repressive wasn't really central to the second amendment, at all. Those who thought otherwise, like participants in the Whiskey Rebellion, were dealt with quite ruthlessly.
Today's mythological construct around armed citizenry vs repressive govt stems from a much later time, the Civil War, and we all know how that worked out. Vague threats of armed insurrection against the duly elected govt will be dealt with most un-gently should they come to fruition. The legitimacy of the govt will remain unchallengeable so long as that is the case.
That reason alone demands the broadest voting franchise possible, which is the basis of true legitimacy.
It's impossible to determine what the founders would have thought about modern firearms, because they had a very limited frame of reference. Their guns were quite primitive, with smoothbore muzzle loading black powder flintlocks being what they had. Rifled barrels were rare, and the invention of the percussion cap, conical bullets, smokeless powder, cartridges & breechloading repeaters lay in the future. The second amendment was intended to apply to arms as they understood them, not necessarily to arms that were beyond their imaginations.