True, but you can't fight a massively distributed attack using a very small concentrated force of professional soldiers; hence the population needs to be issued with weapons and training in an emergency for civil defense. Conventional weapons like tanks and fixed emplacements just become easy targets.

Well then maybe that, too, is a problem that needs solved?

Regardless, a slamfire shotgun only requires two pipes and a nail. Ammo is still an issue, but it's a start.