The idea that you can stop an invading army by having a gun
No, I don't expect them to stop an invading army. I expect they can fend off few looters or would be rapist from said army, hopfully with a help of some neighbours..
too many people who can't even be trusted to operate a chainsaw for cutting wood,
In every society there are about 20% of idiots unable to do anything or to learn much ....there is about 20% of people who are creative and there is the rest in the middle,
There nothing you can do it about,,,playing nana to some poor sod who might harm himself is no way to think about that issue.
Why such a concern should depreve people who are able and willing to defend themselves from ample tools fit for that purpose? As you say they can hurt themselves with a hammer or some other tool, it doesn't matter, why guns are taboo? Guns are only tools...