Nothing to be done about that; it's in their genes. After all, that particular nation was mostly founded on condemned criminals, violent religious fanatics and ne'er-do-wells and misfits and madmen who'd failed to fit in and/or been thrown out of other, more civilised countries; often just before being hanged for some insignificant wrongdoing or other.
All things considered, the law does work pretty well. It is, as you point out, proper crazies doing most of the the mass-shooting, with criminal street-gangs making up the rest. Their normal, ordinary law-abiding citizens behave the same as normal, ordinary law-abiding citizens behave everywhere else. And it's not as though the world is running out of Americans, is it. Apparently there's three-hundert fiddy million of the buggers nowadays and millions more pouring in all the time.
Good luck to them.