I think the reason for the shock is that people tend to forget that, when horrible situations such as this do take place, it is the “spiritual war” between Heaven vs. Hades which is ongoing, made visable, in the worse way possible.
I agree with you. However, it’s also an example of a simply natural failure to reason about our faith or about reality. Why are 22 children shot to death in one school a spiritual crisis, while 22 children shot to death in the same time period, but geographically scattered, are a matter of indifference? Why are thousands of people killed by a tsunami an existential crisis, but thousands of people dying from ... flood, fall, lightning, earthquake, landslide, bus accident ... in the same time period, but geographically scattered, are a matter of indifference?
Our faith tells us that evil acts come from the Evil One, and that every believer needs to oppose evil, spiritually and actively, in himself and in the world. Our reason should tell us that we don’t address a practical problem, such the protection of children, by going hysterical over “snapshot” events. In this way, I think the evil-intentioned reaction, “Oh, what a good opportunity to push gun confiscation again!” is more rational and more intelligent than the good-intentioned, emotional, “Yes, yes, let’s do anything, everything!!! to make sure this can’t happen again!”