I don't like pragmaticism (I hate it). Gun ownership is a right.
But I can give you one pragmatic reason nevertheless: a madman can kill a few dozens. The state can kill thousands and millions. And it has been proven again and again that it does.
I would agree with you, if you said _weapons_ are a right. But guns are too instantaneous and irreversible.
It's almost impossible to stab a friend to death by accident. Accidental killings happen as a regular statistic.
I agree that a state must be kept in check by its civilians, under a danger of violence, but then you have to arm civilians with mobile artillery vehicles and such.
Don't get me wrong - few things warm my heart more than seeing civilians begin to return fire on their aggressor authorities, but that is another kind of issue, than carying a 9mm pistol inside your pocket, so to shoot muggers - or someone walking towards you scarily.
Argue something else, and I'll begin to aggree: Assault rifles in peoples homes, safely locked up. NOT for carrying around. NOT for use while drunk...
The Norwegian "Home Defense" allready issue assault rifles and ammunition to be kept in homes, for quick mobilization. More of this, for example. This would give the people an edge, while they wait for army defectors bringing with them heavy equipment (if not, any resistance is pointless).
Handguns are not enough to achieve this, since they wont even penetrate most modern soldiers armor.