Edit: assuming we are talking about shooting the criminal not just use the weapon as a deterrent. No idea what happens in that case, but I reckon either or both civil and military justice are going to have a word with you.
Calm, reasonable robber--of course you hand it over. Crazy methhead, if he makes a mistake and gives you an opportunity you very well might be better off taking it. America doesn't try to judge the situation in advance.
Drug addicts usually want to be left alone and won't bother you. Exception being people chuck full of cocaine and alcohol in and arounds nightclubs frustrated about not getting layed.
The problem is being tackled the other way around by trying to keep poverty, inequality and thus acts of desperation low.
> They are not allowed to possess ammunition unless in special militias. Any ammunition bought or issued at ranges cannot be taken off premises.
So potentially yes, but only if you mean using the gun as a club.
Swiss gun owners are allowed to buy, own, and use ammunition. They may also use a privately-owned firearm in self-defense situationally, but the legal justification for use of deadly force in Switzerland will obviously be more stringent than it would be in the United States.
https://en.wikipedia.org/wiki/Firearms_regulation_in_Switzer...
So there is a big difference to gun ownership in the US (and elsewhere).
(I'm not commenting on the morality of either state's laws; just pointing out that US states differ widely on gun laws.)
[Edit: I originally said California instead of New Jersey. NJ's laws are stricter but it appears that the vast majority of states allow much leeway when in your own home, so I might even be wrong about NJ.
https://en.m.wikipedia.org/wiki/Stand-your-ground_law
]