It's also a good explanation of how there's already a de facto gun registration in place.
With all due respect, I can think of hardly anything less registration-like than boxes and filing cabinets full of hand-written, misspelled, yellowing logbooks and Form 4473s scattered through the back offices of every gun shop in our fair land.
Is the system remarkably efficient at turning up the whereabouts (or at least the origins) of a gun that has been manufactured recently and hasn't changed hands too many times in the private sector? Yes.
But as for it being used as a "registry" or some "master list" of gun owners, the Powers That Be would be better off using the phone book.