Let's think about the need for weapons to repel an out of control government coming for YOU.

[Lizzie Poppet]

14. If you're facing an intact US military, you're screwed.

Not any reasonable doubt about that. And that's what would happen in any Waco-like situation that escalated beyond the ability of law enforcement to deal with...

But what about scenarios of actual widespread insurrection? A civil war, but not in the pattern of our own 19th Century version (with an attempt to form a separate nation), but something more like, say, Syria? Would the US military remain intact and fully under the control of the civilian government in such a scenario?

I'd say that's actually very unlikely. Any cause for such a widespread insurrection, one that had a significant percentage of the people ready to violently oppose the government, would also be a cause that applied to members of the military and their families. Their response to such a cause would more-or-less mirror that of the general population (with some consideration given to the rather conservative lean the current military has). Some would sympathize with the insurrectionists, some would e loyalists. Military training and discipline is NOT going to override those loyalties if the reason for the insurrection is sufficiently compelling.

The result of this spread of opinion would be the fragmentation of the military. It would in some cases split onto opposing factions, but I suspect the more common result would be fragmentation of entire units due to massive defections and AWOL incidents. Defectors would tent to try to take at least personal weapons and easily-transported systems like mortars and man-portable anti-aircraft weapons with them to the other side. The most complex and logistically-demanding systems would fast become unusable.

We have seen similar situations play out in insurrection in other nations. The government forces have an initial advantage, as more of their modern weapons systems remain operable. But at some point (and if they don;t achieve a rapid victory while those systems remain in the game), lack of logistic support starts to even the playing field. At this point, civilian arms tend to have a considerable influence, as the fighting begins to be more of a matter of opposing riflemen and such than of aircraft, armor, artillery, and so forth.

Hopefully, it never comes to this here. I'd expect a much more peaceful dissolution of the Union to be what really happens when this nation as currently constituted runs its course.