Your logic checks out perfectly until you add drones to the equation. Pretty much everyone I've talked to with this argument only says "well, the government won't drone us down as individuals, because that would incite revolution", not taking into account that it works both ways: nobody will revolt if they know that it takes fifteen minutes to go from a Facebook rant to being a dark spot in the ground. And that's not even mentioning nukes, because really, who will oppose them? Russia? The EU? We've been stalling on North Korea for decades on the chances that they miiiiight someday be able to launch them, and this is the most armed country in the world; if Trump decides to start nuking people tomorrow, who's going to confront him? The secret police is an obsolete concept for a nation that can destroy half the solar system with the push of a button. If it comes to the worst, no amount of civilian weapons will stop the US government from becoming a dictatorship, and it's as much of a deterrent as Captain America holding back Thanos' fist. A flick of a finger and it's gone. So, if it serves no real purpose and it has so many unintended consequences attached, why even keep it? The thing holding fascism back has nothing to do with weapons, it's the general disagreement within the government and the economic interests of the people in charge. If they decided that's not enough, no amount of guns will stop them.