This is a common belief in the US, and it has one obvious weakness: what if most of the people with guns are happy about an authoritarian government, since they feel like they are the "in-group", and they hate the "out-group" anyway?

I mean, the erosion of civil rights in the US has gone on for some time, and the argument that guns would prevent it is constantly proved wrong. As long as there's lip service to free speech, and more importantly, the right to bear arms, it seems that all other rights can be trampled on with impunity.