An unloaded firearm is a hammer if the person you're pointing at knows it's unloaded.
But I wasn't talking just about an unloaded firearm. If you've got a gun with one bullet, you can hold people at bay until they get desperate enough. A machine gun with a full clip, and even desperation won't do it for most people.
Point is, when a totalitarian regime is exerting control, cars are easy. Just cut off the fuel deliveries. Taking away guns is a door-to-door affair, and they're small and easy to hide.