Political Memes

Realistically, in any overt civil war against a despotic US government, the rebels lack of serious military equipment would be a very short term problem. Look at the Syrian Civil War. Do you think in any future US civil war, outside powers wouldn't be involved? If there was a serious armed insurgency against a despotic US regime, do you think there would be any shortage of outside powers smuggling in heavy weaponry to aid the resistance? The US does not exist in a vacuum; foreign powers would be involved. Some would do so because they actually support the rebels. Some would do so simply because they see the civil war as a way to weaken US power. You could have the odd situation where both Europe and China were sending weapons to the rebels.

Now the government will always have the brute force advantage; you're not going to smuggle 5th generation jet fighters or main battle tanks across the border. But combat drones, surface to air missiles, RPGs, and any other sort of man-portable military-grade weaponry? The US would be awash in those things pretty quickly. As we've seen in Ukraine and Syria, those can have quite an impact. Oh, and this is before you consider the possibility of rebels using civilian-grade weaponry to raid military installations and seize military-grade weaponry. And there would be no shortage of veterans and defected US military members who know how to use those heavier weapons with great effectiveness.

And while the government has the real firepower like artillery and nukes, those are a lot less useful in a civil war than in a conflict against a foreign nation. The US government can flatten a foreign city without harming itself. But every time it uses heavy weaponry against US cities, it undermines its own legitimacy, breeds more rebels, and degrades its own economic capacity.

Rebels are not going to topple the government with AR-15s. But rebels can use those to obtain much more powerful weapons, both seized from US stockpiles and obtained from foreign governments.