I think the OP means black swans happen. And so terrorism should be considered a black swan sort of risk. But if we're doing that then shut down all the various financial institutions that may cause such risk as they have been shown to do more than once in the past. However, thus far the black swan risk from terrorism seems to be a few thousand people in the time frame of around two to three decades... globally. The cost seems to be in the trillions but that has little to do with the terrorists, and much to do with the management of the response to terror... and also management of the risk posed by it.
Globally? No, that's a very USA-centric view. Terrorism has killed hundreds of people globally this month alone. It has destabilized (if not outright destroyed) many countries over the past 2-3 decades.
Terrorism has not destroyed countries across the past 2-3 decades.
Civil wars did. Many of them have either been started by, or fueled by American foreign policy.
So, yes, your country being destabilized by a civil war is a real threat if you live in the global south. In America? It's not going to happen because of a few mouthbreathers decided to cook some bathtub C4.
Yeah it has killed hundreds this month mostly again due to mismanagement of response to terror and management of the prep for terror. It's a significantly different thing to compare terrorism in 3rd world countries who are routinely targets of both non-State and State sponsored terror because lack of control mechanisms and terror in developed countries or countries with stable governance systems.