The issue is that car accidents are accidents (often involving negligence), whereas gun crime is generally willful (sometimes involving crazy people, but generally just criminals).
There's the issue that a lawful collector or random hunter or whatever with lots of guns is a lower risk than a gangster with one gun, and the risk per gun is vastly lower for a law abiding person with lots of guns vs. a bad guy with one or a few.
In fact, I'd bet that gun crime goes down as the number of guns possessed goes up. Obviously 0 is the least, but 1 is the most, and it's probably close to exponential after that. The guy with 31 guns is way less likely to kill someone than the guy with 3.
The only risk when someone has lots of guns is that they'll get distributed to others -- either through theft or through willful straw-man purchase or other distribution. A person who holds ~30 guns for a gang, then distributes them as needed for crime, is a problem, yes.