It seems like a lot of the shootings that aren't gang related happen because someone just flips out. Take the gun away from that person and they probably go home, have a wank and get over it. They aren't murderers that would have access to an illegal firearm, and they aren't murderers that would find another way to kill. The same could probably be said for a lot of the suicide victims too.
We've probably all been in a situation where we've lost our heads, punched someone or shouted in a fit of rage or something. I know I have. I'd like to think I would never shoot someone, but if I had a gun on me at those times, who knows. And that right there is enough for me to support a ban - sure it wouldn't stop a lot of killings, at least not right away, but for every gun off the streets you're potentially saving a life, if not dozens of them.