You said it, why not simply treat guns like cars, with licensing of user and registration of device. Then there's a responsibility and liability filter. I don't suppose that the public would begrudge a bunch of highly trained/responsible non police/miliary people carrying concealed weapons, given they would properly use these weapons and be responsible for any misuse. They would augment the police/military, and that right there is probably what the founders meant as "well regulated militia"