Oof. Your estimates of the power of 300 million people to overcome a military 20 million strong do not match mine. If we're assuming complete consolidation of groups (i.e. those 20 million wholly aligned against the 300 million)... Modern warfare is entirely asymmetric. It depends on how willing that military would be to deploy air power, bombs, and smart weapons. To say nothing of how much organization of such a resistance could be stymied by the simple expedient of shutting off the grid (electrical and communications) that could occur in an open civil war.

... in the abstract. I hardly imagine it'd come to a shooting war over something like the perpetual push-pull of figuring out what "privacy" is. That's a conversation that's been going on for hundreds of years.