A better analogy would be a passport. It doesn’t stop all terrorists from boarding a plane at lest it stops already know to authorities ones (unless they have a passport on someone else’s name which is not easy).
I forgot the name of this fallacy, I read about it in Nassim Taleb’s Antifragile a long time ago, but basically being wrong at spam won’t cause a lot of damage while being wrong once about a terrorist may cause thousands of deaths