Wow, so that means this guy actually prevented a tragedy! That's...!
No, wait, that means he still killed 26 people, which is just the latest in a line of mass shooting incidents several thousand long (and counting) that "Good guys with a gun" have failed to prevent.
Civilians don't carry guns to "prevent tragedy." They carry guns to protect themselves and the ones they love. That's not my opinion. That's the actual law. The people who have concealed carry permits are NOT allowed to simply start shooting whenever someone else goes berserk in some attempt to "be a hero." Simply put, if I (or any non-officer) shoot someone and can't articulate how it was directly to prevent severe bodily harm to me or a loved one with me, then I'm the one who's going to face criminal charges.
Most people who actually have a concealed carry permit would already know this. Of course, some states allow "open carry" without any permits, but even then many of the same laws still apply when it comes to self-defense.
In many cases, you actually can shoot someone if they are actively targeting the public. In most states that offer concealed carry, you would be justified in stopping a person from shooting innocent people. That's precisely what happened in Texas when a neighbor shot the assailant.