"A well regulated militia" as most people understand that phrase, is a militia that would most likely be owned and directed against independant citizens by a tyrannical government. We've already witnessed the "security" requirement for tyranny.
Early citizens had direct experience with tyrannical overreach. And a strong distaste for it.
The second amendment is about weapons parody for the true sovereigns of any country, its citizens, who should have access to any weaponry they are likely to confront in the hands of mercenary goons from an emerging police state.
It allows those with the sand to fight tyranny the tools to acquit themselves well.
Americans in the future may have the sand to fight, they'll have the need for an unneutered second amendment. Anybody can lose or die, fights are for winning as dirty and unfairly as possible.
I'm in Phildelphia, old men on street corners downtown will sell you a durably bound copy of "Common Sense" for a buck. It's a good book. It happened.