I lived in Japan for a number of years, and they have just as much mental illness as other countries. You know what they don't have? Mass shootings. Or any shootings for that matter. Sure there is the occasional suicide by train or wild person wielding a kitchen knife, but impact is severely limited by comparison.

Take away the guns, and you fix the gun problem. And before anyone flies off the handle about 'I have to protect my family!' Just remember that a staggering number of gun-related domestic violence and death (by suicide) in the US is also due to guns. You have a better chance of protecting your family by not having a gun in the home than you would fending off any would-be attackers.