That's already how this works in some countries. If someone attacks you with a baseball bat or fists and you shoot them dead you might be sentenced for overstepping a reasonable self-defense. The same crime at gun-point and at knife-point carries much harsher punishment. This encourages reasonable (de)escalation instead of just going for 120% from the start. And saves lives.
End result is - even in countries with relatively easy access to guns for hobby - nobody carries them for self-defense (criminals included), because they don't expect to need them, and in case of a self-defense situation they are more likely to cause problems than to solve them.