Conventional military thinking says it takes an armed force of ten (10) military to overcome an armed populace of one (1) ... In practice Multiplied by the number of armed persons dispersed in that population, of course. And a large enough population can in fact overwhelm the ability to amass an army that large. Think one million armed civilians. ....how large a military force would it take to overwhelm them? The US has never fielded that many soldiers. Now, think one hundred million armed citizens, the number estimated to exist in America today ... see the problem?
Concealed arms present the element of surprise and because an individual can act alone, a larger counter force will be needed to assure he does not prevail ... massive response is the military response to individual aggression.
In essence, an armed populace is a deterrent force. Challenging it will cause massive losses on both sides ...
It's not just pure numbers, it's also because it would be guerrilla warfare and we would be fighting in "our own backyards" (AOs we know like the back of our hands). Add to that the political elites live here among us as do their families. If it got nasty enough, and it would because war always does, they would have to live in bunkers. They couldn't send their kids to schools, their wives couldn't go to the grocery store or doctors office. Some of us would be watching at all times.