[argumentum]

You say "over-react", but in many ways the reaction is quite rational. When an airplane crashes, hundreds of people die. We are reacting not just to our fear of dying in a crash, but out of sorry of the lives lost and empathy for their families.

Humans also tend to react much more strongly to the malicious actions of others than to the arbitrariness of nature (including human error, as humans are part of nature). Even compared to your ordinary murder, terrorism takes it to the next level, since it indicates that there are others who share the ideology or membership in the terrorist group who intend to cause harm to your society, and they're still out there.

In short, it's not all about "risk". It's about justice. There's little irrational about the desire to live in a just world, and the willingness to pay for it.