This. Even if they outnumbered, say, a platoon of Marines sent in to confiscate their guns, it would be a very short, very one-sided fight. The Marines are trained in group fighting tactics while the nutsos are islands in a storm. They'd be individually overwhelmed very swiftly. They're mostly too paranoid to work together.
By the time you're treating a civil issue as a military one you've failed, game is over.
Seriously this.
The "why don't we just kill them" mentality never works, for reasons you have explained. You don't turn the weapons of a country against the people they are made to protect, because when you breach the social contract this critically, all bet are off and your government loses its legitimacy.
Just to add to your exemple, the whole bolchevik insurrection can be traced down to a single event, which are the troops of Nicholas II opening fire on a religious protesting crowd. A very limited percentage of the russian people had red sympathies, but having imperial troops slaughtering people on the street is a picture everyone understands very, very clearly
The people you want to kill have families, sympathizers, people who understand their cause. You want to disarm them and to judge them according to the rule of law for the crime they have commited, and not to treat them as an enemy faction.
People by in large understand the difference between a criminal and an enemy. Those are two different categories and I do pity the politicians who will come to forget the distinction