"But if you try to overthrow the government, suddenly all of that power will be united against you, and you will not stand a chance."
What makes you think many parts of this very un-unified government (you didn't even get into federalism including state and local divisions of labor) won't also be on the side of those wishing to overthrow it?
Let's just look at my home town of Joplin, Missouri, in solidly Red State America. Only a few hundred police for 50K residents; as a hypothetical, what do you think would be the difference between their revolting alone, vs. with thousands of just as well armed civilians? Who's RKBA they strongly support, in words and deeds, I might add.
What makes you think many parts of this very un-unified government (you didn't even get into federalism including state and local divisions of labor) won't also be on the side of those wishing to overthrow it?