The hypothesis that guns are a deterrent has little to do with the citizenry fighting against the army or the police. It is about the risk of political assassination by a rogue individual every time a politician walks outside. If the leaders start to deviate significantly from the will of the median person, that risk goes up by a lot, hence the deterrent effect. Would Kim Jong Un still be around if every person was armed? Perhaps, but it'd be quite a bit less likely.