When you invade somebody and lose - you return to status quo (with some bad diplomatic consequences but still). There's a point past which it doesn't make sense to escalate.
When your citizens try to overthrow you and you lose - you and your family are dead soon. There's no thing that autocratic government won't do to avoid being overthrown.
As for fantasies of gun rights preventing fascism - it didn't historically (see Italy where before Mussolini the gun laws were very loose). Nor did fascism necessarily resulted in stricter gun control (in Germany Hitler actually loosened the gun laws after he took control). It frankly doesn't matter.
The simple fact is - in a developed country uprisings have 0 chance of winning against a professional army. Hand guns change nothing. The only way to win is to persuade the army to take your side. Which usually happens when the country doesn't have enough money to buy their loyalty.
US police officers kill about 1000 people a year, guns don't seem to protect them.
The narrative of armed citizens operating in a structure to defend citizens and the constitution works fine if you don't have armed citizens operating in a structure to defend citizens and the constitution.
If you lose hearts and minds of one group armed US citizens (the military), why is your group of armed citizens any more justified?
If you don't lose it, why do you need the armaments?