This post goes out to Robert Hewes, who said in comments to this post:
The only incident I can think of off-hand (where a CCW carrier thwarted a mass shooting) was the New Life Church shooting that was ended by a parishioner.
These incidents happen all of the time. They just don’t make the news. A mass shooting that doesn’t happen thanks to a CCW holder just isn’t bloody enough to make the news.
For example, Aurora had another attempted spree shooting two weeks before the Batman shooting:
There is also this shooting, where an armed robber was herding the employees into the rear of the store, and was stopped when the manager shot him in the face. While we don’t know that the robber intended to herd them into the back in order to massacre them, it is certainly probable.