Wishful thinking, FRiend, on several counts.
First, you're assuming that all 100 million poorly-armed folks will be against the government. Doubtful.
Second, of those who oppose the government, you assume that all of them would actually take up arms even if they had them. Again, doubtful.
Finally -- and this is the big one -- a 2 million man army capable of reliably killing their attackers in many or most instances will quickly take the fight out of the vast majority of those who oppose the government.
As we've already shown in Iraq and Afghanistan, large concentrations of enemies are almost certain to be destroyed. An insurgency would quickly devolve into individual or small-group attacks that are primarily annoying rather than militarily significant. But those, too, have become much less successful over time.
Finally, modern counter-insurgency tactics would work in a civilized country, as well or better than they have in Iraq. The ability to sustain an insurgency is doubtful.
It's not to say that an insurgency couldn't be successful ... but the mismatch between government and potential insurgents is unbelievably greater than the Founders could ever have imagined, and it's increasing every month.
“As we’ve already shown in Iraq and Afghanistan, large concentrations of enemies are almost certain to be destroyed. “
Let’s see, 5+ years later and we are still at it in a small region of the world about the size of California with only a few cities against many who can’t even read.
Here in the US you have millions of educated and military experienced Americans who are extremely well armed and scattered across an entire nation. Good luck with that attack against us.