It could be much simpler than that. People as a collective massively over-react to spectacle of terrorism in similar ways to how they over-react to the spectacle of airplane crashes (you are far more likely to die each time you drive to the grocery store than from a flight around the world).

Politicians have adopted a "Under my watch: zero tolerance for any risk at any cost! ANY. COST." approach because no one wants to be held responsible for anything slipping through at all. It's not about saving a few hundred lives (vs tens of thousands/year in car crashes). It's about denying responsibility by spending other people's money. It's a redux of "No one ever got fired for buying I.B.M.". This way, when something bad does happen, they can point to the massive over-spending they already did and say "Don't blame me. I did far, far more than was reasonable. What more do you want from me?"

You 5 points are valid, but IMHO they are the grease that gets the rest of the machine to cooperate. I think a 5-why's approach would lead back to the politician's fear of reactionary voters.