Do criminals care about gun registration? Of course not. But it damn well WOULD matter to those who legally buy firearms and privately sell them to criminals. Why? Joe Criminal commits a crime, and is caught - and law enforcement sees the serial number on the firearm, and sees who legally purchased the gun in the first place...and then goes to that original owner: "Sir, you got some 'splainin to do."
With registration, gun owners are responsible for what is done with their firearms. They can only sell them (privately or not) to someone who passes a background check. If the guns are stolen, then the gun owner needs to report it.
And as a direct result, the easy availability of firearms to be bought by criminals begins to not be as easy anymore.
Gun registration does not significantly hinder the ability of law-abiding citizens to purchase firearms. It DOES hinder the ability of would-be gun smugglers to get their hands on firearms to sell to criminals...and if you don't think this is a big deal, remember that
nearly a freaking quarter-million firearms are smuggled FROM America TO Mexico each and every year:
Some 2.2 percent of all US gun sales are made to smuggling rings that take firearms to Mexico, a scale of illegal trafficking that’s “much higher than widely assumed,” an academic study released Monday found.
An average of 253,000 weapons purchased in the United States head south of the border each year, according to the study by four scholars at the University of San Diego’s Trans-Border Institute and the Igarape Institute, a research center in Rio de Janeiro, Brazil.
Profit margins at many gun stores are razor thin, and thousands of US gun vendors would go out of business without the illicit traffic to Mexico, said Topher McDougal, an economist educated at the Massachusetts Institute of Technology who’s one of the study’s authors.