In the United States, we have a definite split of opinion on gun control. Three of the Democratic contenders – Bernie Sanders, Hillary Clinton, and Martin O'Malley – have proposed specific reforms. None of the Republican contenders have so far.
Taking all of the Democratic proposals together, these appear to be the important reforms:
Universal background checks on buyers, eliminating the present loopholes for gun show sales. A sale could not be completed unless a background check is done, no matter how long it takes (presently, if the check is not completed within three days, the sale can go forward – that's how the Charleston shooter got him his gun, despite his earlier felony conviction).
“Straw purchases” (where one person buys a gun for another) should be made a federal crime.
Anyone convicted of domestic abuse or stalking should not be allowed to own a gun.
Anyone obtaining a gun (whether by sale, gift, or transfer) should have to get a finger-print based license and complete safety training.
Minimum age 21 to own a gun.
Safe home storage for guns should be legally defined and required.
Persons who are mentally ill should not own guns.
The federal law (“Protection of Lawful Commerce in Arms Act”) that prevents victims of gun violence from suing gun manufacturers or dealers for damages should be repealed.
There should be a national firearms registry.
Semi-automatic weapons should be banned (except for police and military use).
All of these are good suggestions. But people in many (particularly rural) states may disagree. So why not enact broad laws but allow states to “opt out” of some of them? If a state wants out, it can change the law within its own borders. However, all guns anywhere would need to be registered nationally, and any transfer of ownership would need to be reported to the registry. Furthermore, the transferee of a gun would have to be identified by a driver's license or other governmental identification, and only a resident of a state could buy a gun within that state, even if the state had otherwise “opted out.” If a gun owner moved from one state to another, he would have to comply with the law in his new state of residence so far as gun ownership is concerned. Each state could pass its own gun restrictions, ones that were more or less lenient than the federal law. (Personally, I think that a ban on semi-automatic weapons should be national and not subject to the "opt out." But the meaning of the "opt out" would certainly be subject to negotiation).
With an “opt out” provision, any state could do what it wanted within its borders. And this sort of provision might encourage conservative politicians to vote for the law, knowing that their state could opt out of most of the provisions if it chose to do so. In other words, states that wanted strong gun control would probably not opt out (unless they felt that more controls were required), and those that felt that they wanted less restrictions could opt out, adding whatever restrictions they wanted. However, all guns would be registered nationally, and guns could be transferred only to residents in the state. This would prevent residents in restrictive states from buying guns in lenient states.
The opt out provision has been used in federal law before. Under the bankruptcy law enacted in 1978, there was a federal exemption law for debtors. People filing for bankruptcy could elect the federal exemption law or the law for exemptions in their own state. Married couples could each elect separately. But states could opt out so that bankruptcy debtors could only elect the state exemption law.
The reason for the opt out provision was to permit states to see how the bankruptcy law would operate with a federal exemption provision. Under the prior law, exemptions in bankruptcy were only the state provisions. Congress permitted the states to go back to that system or to leave the choice to the debtors. Many states did opt out. Some tried to adopt special state exemptions applicable only in bankruptcy, although these were generally found to be unconstitutional, as bankruptcy is exclusively a federal power. The general idea of the opt out presumably made the bankruptcy law more acceptable to creditors and allowed for its passage in 1978.
Gun control with an opt out provision would make the law more acceptable and would established the all-important federal registry for guns. It could bring consensus to an issue where consensus eludes us.