Actually, I could argue the case for having the permit and a firearm 'just in case'.
But it wouldn't be a casual strategy. You'd have to include practice, training the family in firearm use, having a backup firearm and just using the firearm in the house.
Though on the surface it would look like a person who wasn't fearful enough, wasn't aware enough of the dangers 'out there', in reality it could just be a transparent, but effective and well-thought out regime. It would include basic fortifications, doors, windows, alarm, motion-detection lights, taking care entering and leaving (where the danger of not carrying on the person is most evident).
I think statistically, proper use of a firearm to defend the home where you can't retreat, can't escape easily, need to protect (sleeping kids) is where a majority of people could bolster their SD plans with minimal difficulty and not feel they live in a dangerous society. If we listen to our 'senses' we know how to avoid danger out there early enough to avoid them in many cases.
I feel you'd have a self-defense solution for 99.9% of events you might expect to encounter.
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Where it breaks down is where society is weakest. The young, the weak, the females, elderly and disabled need to be allowed and enabled to have protection out in the world where they are the first targets.
FWIW