This is the point that I always make when the "utility" argument is brought up, "since gun use is really rare" to some people.
Consider guns are non-existant. Something equally as likely to happen, what if the shooter at Newtown decided to run all of the children over outside at recess? What if the Aurora shooter thought the same thing as a huge mob of people waited outside for the movie? Would we now ban vehicles, because we can't trust YOU with a vehicle? Or "I'm sorry, would that be too inconvenient because it applies to YOU?".
Also in both cases (equally as likely) that they decided to quietly and quickly bar the doors, and proceeded to set the building on fire? (I promise that fire suppression system companies would be dissolved for how ineffective the systems really are). Then what now? Do we remove all means to create fire? Remove all accelerants from life?
If he still disagrees you should invite him to a range. Once he has a blast with your little tube-fed .22, remind him that you can fit more than ten rounds in it and it'll be illegal.