I don't think an argument by example works here... it's obvious that anyone with a gun can kill any number of people. I think what Drak means is that there are an excessive amount of guns in America, which to some degree (obviously) plays a role in gun violence in America.
Problem here is that guns are ingrained into the country and has become part of the culture. There is no way in hell that it will change anytime soon... Gun lobbyist, NRA, politicians etc will not let that happen. It's part of the constitution.
Problem 2 is that Americans hear and see more and more gun violence and believe that owning a gun or carrying a gun is the only solution, so the cycle continues.
Trust me, there's no argument to win here. No logic involved, it just is what it is.