Mandatory auto insurance deters the most irresponsible and destitute from owning cars, so the same would hold for firearms.
Geez... You need to get out more. MANY people are on the road in untitled uninsured cars. My boy sold a truck, and several years later, was called on the phone and instructed to get that truck off the side of the road, or it would be towed.... He was the last registered owner, and no paper, no insurance, was carried on that truck in the meantime.
And do you mean to say that the destitute do not have the right to defense?