Patri Friedman at Catallarchy observes:
Anyway, I am not claiming that any one story (or in this case, four stories) prove anything about the overall tradeoffs. But these stories are in direct contrast to explicit statements some of you have made about how you think the world works. So please realize that you were wrong, and that guns are demonstrably capable of stopping massacres short. Doesn’t mean we should have them, but it is directly relevant to yesterday’s incident. We don’t know what the distribution of death reductions would have been if the massacre hadn’t been in a gun free zone, but it surely has a non-zero mean, and quite possibly a significant one. After all, this was an extremely bad massacre, which means more people involved and more time to get armed.
But of course, probabilistic lives saved by guns are vastly less visceral than actual lives ended by them, hence much more difficult for us to view as real.