At some point presumably there is a carrying cost to all the what-if scenarios. If your body contains/maintains a whole host of organisms going around checking

At some point presumably there is a carrying cost to all the what-if scenarios. If your body contains/maintains a whole host of organisms going around checking whether an unrecognised something is 'one of these bad things' eventually you're going to run out of spare energy to do other basic tasks. At what point does this become optimised to "you're probably one of these, therefore I exterminate you"? Note that when that system goes wrong you could end up in auto-immune disease land, or somehow eventually copy informational mistakes/signals land (cancer). This is my overly-simplistic view though on limited understanding, I am not a medical professional.