These shooters aren't the sharpest tacks around. They're relatively rare... a tiny tiny fraction of the murders in this country. It requires a special confluence of crazy, misanthropy, and basic technical ability... many people have one or two of these. Few have all three.
Now, I'll readily agree that since there are millions upon millions of semi-automatic assault rifles out there, it'd be a herculean task to control those. It's be a long time befor such a.law would be effective.
But once fully implemented... why would it be any different than laws restricting full auto weapons?
just because you can. it's overated. only the military need it. some of the best guns i owned were single shot .22lr . and single barrel shotguns. you learn to shoot straight when you have only one round . 12 rounds a second from an armaltite or ar just pisses of your neighbous. they should have told me