I can accept getting heart disease—maybe it was my fault?—much more readily that being actively, senselessly, killed by someone else. Terrorists know this too, which is why definitionally terrorism is meant to induce fear by way of its unpredictability.
You wrote "security theater" to imply that we shouldn't attempt to address terrorism and school shootings because they don't kill enough people. I think that we ought to fund research into good, effective, ways to reduce gun violence _because_ it's something that we don't control ourselves.
"There is only one way to happiness and that is to cease worrying about things which are beyond the power or our will."
-Epictetus
I can control my own actions, so my worry about heart disease can inform my dietary choices.
We can control gun violence by influencing culture or changing laws, so gun control is an appropriate subject of worry.
We cannot control the sun going supernova. We shouldn't worry about that.
(i.e. Things I can't control as an individual, we as a society might still be able to control or influence.)
If you think people are being overly emotional over these issues try to imagine a plausible reason why.
And that was because of the misguided emotional response (i.e. invading countries which had nothing to do with it), not because of the event itself.
I welcome more research on effective ways to reduce gun violence, but unfortunately ( https://en.wikipedia.org/wiki/Dickey_Amendment_(1996) ) researchers have been prevented from doing so.
The clear, most effective way to reduce gun violence is to reduce the number of guns. (cf. every other developed nation.) However, the current interpretation of the 2nd amendment seems to make that difficult.
Just like we forced people to stop drinking during prohibition, and we force petty criminals all the time to stop doing bad stuff once caught?
We'd like to think it's the former ("we can, but we don't"), but the reality is we can't.
We are incredibly ineffective at doling out scarce resources or pricing in externalities.
I just don't expect humanity to get a handle on it for another 100 years at least. I'd say that, right now, we can't.
In cases like these I like to take the Freakonomics formula for risk, that outrage factors more into observed risk than actual danger.
We're more worried about Terrorism than Heart Disease, even as we have far more control over the latter.