The way I see it, a populace which exercises the RKBA has a protection from a government which already wields substantial (if ill-gotten) influence over their lives. Put simply: it's much harder to force an ARMED citizen to submit to your demands than to force an unarmed citizen to submit.
Here's an article from JPFO which puts it much more elegantly than I.
As a teaser, here are the title and first two paragraphs of the essay:
"Why the Gun is Civilization
By Marko Kloos
Human beings only have two ways to deal with one another: reason and force. If you want me to do something for you, you have a choice of either convincing me via argument, or force me to do your bidding under threat of force. Every human interaction falls into one of those two categories, without exception. Reason or force, that’s it.
In a truly moral and civilized society, people exclusively interact through persuasion. Force has no place as a valid method of social interaction, and the only thing that removes force from the menu is the personal firearm, as paradoxical as it may sound to some."