They're not especially threatened by citizens permitted to own firearms either. Do you really think that the average gun-owning homeowner can go toe to toe with a soldier who has armor support, air superiority, years of training, and, most importantly, modern military logistics backing him up?

And before you bring up insurgencies, let me remind you that successful insurgencies are marked by two features: 1. the occupying army does not speak the same language as the locals, so intimidating translators is an easy and effective way to deny the occupier situational awareness. 2. There is a bordering country willing to support the insurgency with either arms, safe haven, or both. Neither point applies to the US homeland.

Arguably, the last time an insurgency tried to take on the US Army was during the Civil War. Even though both sides had similar quality armament (and the South had higher quality leadership), the North won, thanks to its much stronger industrial base and better developed logistical system (i.e. railroads). The situation is even worse today. The average homeowner does not have easy access to any armament substantially note powerful than an AR-15, and the chances of any branch of the federal military defecting to support a civilian revolution are vanishingly small. In addition, the military speaks the same English that we do, and I'm pretty sure that neither Canada nor Mexico is willing to furnish you with arms and/or IEDs. So, with all that in mind, would you care to explain how, exactly, the Second Amendment protects me from the US government becoming a tyranny?

People often talk about the impossibility of armed revolt in a modern nuclear state. "You'd be killed on the first day," they tell me (not that I'm advocating armed revolt here, just to be clear). What they forget is that an armed revolt in the United States would still be chiefly a political act. America would have the eyes of the world on it, and there would be propaganda from both sides. America of today would be hesitant to bring the full force of its military down on a militant group if the group could successfully paint themselves as freedom fighters.

This would only work if the revs were in response to a truly tyrannical act, say if a president were to declare a state of emergency and indefinitely suspend elections. Think of the Arab Spring, Waco Texas, or the negative response to police brutality on the OWS protestors. Think of the imagery (and it would of course be filmed) of a hardy group of patriots facing off against tanks and bombers. These are powerful political images and could bring in diplomatic pressure, outside military aid, etc.

I'm not saying a revolt is likely likely to succeed, I'm just saying it more complicated than a cut and dry, "they have bigger guns, so the revolutionaries lose."

That's true. I was making the point (contra OP) that your owning a gun has little to no impact on the government ability to oppress you. Widespread gun ownership is not some magic pixie dust that will keep the federal government from oppressing us, and strict gun regulation is not some kind emasculation that will prevent the citizenry from rising up against a tyrannical government (c.f. Egypt, Libya).