It's not just killing, it's what a gun represents. Not sure where you are in the U.S. but here in Los Angeles there has been an uptick in crimes where the criminals brandish guns but don't use them. Someone pulling up along side me walking on the street and getting out with a hammer/knife/fists, I can just run away. Registration would help police when a gun used in a crime is recovered, which is my reasoning. Licensing perhaps wouldn't have that much more of an impact unless it's tied to required education, I acquiesce to you on that matter.

This isn't too important but https://www.statista.com/statistics/195325/murder-victims-in-the-us-by-weapon-used (not sure how accurate that data is, but seems to be referenced a lot) shows handguns/firearms not stated are definitely the lion's share of homicide's and FBI's crime data explorer at https://crime-data-explorer.app.cloud.gov/pages/explorer/crime/crime-trend puts "Blunt Object" (which I assume a hammer would fall under) as the 5th most common instrument used in violent crimes, with "Personal Weapons" as #1, "Handgun" at #2, "Knife/Cutting Instrument" as #3 and "Firearm" at #4.