Questions about school shootings

There are a lot of varying factors here which makes answering your question difficult.

You seem to be asking, "What is the impact of an intervention which saves a single person from a school shooting?"

The fact that you mention trauma and increased social impact due to motivation suggests that you mean "saving a single person from a school shooting while the shooting is happening" as opposed to "saving a single person from a school shooting by making school shootings happen less." Such measures would include, for example, increased classroom safety training for students and teachers, or speeding up police response times, but not include preventative measures, such as advocating for gun owners to keep their guns locked in a secure place and not loan them to others. Is that what you're asking about?

Why is this post being downvoted?  I seriously doubt that EAs working to prevent school shootings would be cost-effective, but I don't get why there are downvotes here -- it's a fair question.

Why is this being downvoted? It doesn't seem like a terrible question.