This isn't about outlawing guns. It is about licensure, a time tested means for identifying a legal gun and its owner. It doesn't surprise me, even given the ease at which guns travel from state to state, that a city that requires licensure of its residents will, all other things being equal, tend to have less gun crime than a city that does not. At the very least, cops have the ability to cite an individual for having an unlicensed gun, and to remove that gun from circulation.
What we need are more studies that can differentiate between bad gun laws and those which are actually efficacious. No one wants gun laws that penalize lawful gun ownership and use.