While I agree with you that small groups of citizens foolish enough to engage US government forces in set-piece battles would be wiped out in short order (and good riddance to them...), think about this:
Afghanistan is about the size of Texas, and it has taken much of the might of our nation to just barely keep the lid on over there.
If large numbers of the citizens of the United States decided violent resistance was called for, there are not enough police and military in this county to keep things under control. Those rebels would be living among us, with easy access to the family members and friends of government, police, and military forces - they wouldn't be safely overseas. You couldn't bomb their cities. They probably wouldn't be so nice as to secede as a group of states, and invite Civil War 2.0.
Look at the trouble a single lame sniper team did to the DC area a few years back:
http://en.wikipedia.org/wiki/Beltway_sniper_attacks
Multiply that by...a lot.
Then consider that some of the rebels probably would be clever enough not to use guns...
It would be horrid, who wants that? Why even go there?