The "provably not the Founders' intention" part is the one where you're wrong, and the court opinion specifically discusses this, which is why I recommend that people read it before jumping to conclusions.
By the way, one thing that's often forgotten is that 2A itself was merely an adaptation of similar clauses in state constitutions at the time (many of which explicitly spelled out self-defense as a motivation). At the same time, the original Bill of Rights was all about limiting what the federal government can do, and didn't originally limit the states at all; it was assumed that the respective state constitutions would take care of that, presumably, by expressing the will of their citizens through their own democratic mechanisms. So it's no surprise that the discussion focused mostly on militia - that was the primary concern of the states wrt potential federal government overreach.
When 14A was ratified, and then BoR amendments gradually incorporated against the states, the courts had to reinterpret them accordingly. For example, 1A says that "Congress shall make no law ...", for the same exact reason: the people who wrote it were originally concerned specifically about the power of the federal government. But today, we interpret it as applying to state governments as well, and rather more expansively - and I would hope you'll agree that it's a good thing!
BTW, you seem to be unaware that pro-gun sentiment is alive and well outside of the radical right today - it didn't end with Black Panthers. Some prominent examples include John Brown Gun Club and Huey P. Newton Gun Club.
