The 9-11 attacks were profoundly disruptive in economic and social costs. Just in direct costs like buildings being knocked over, air travel being stopped, being not being able to get to work, was 200 billion dollars.

That's a little less than the GDP of Finland wiped out in one attack.

That is not to mention the cost of fighting the war on terrorism. All in it probably cost 5 Trillion.

You could say, hey, we didn't need to fight the war on terrorism. But the attacks were world changing events for the US. They caused fear, anger, confusion, and a need for revenge.

Whether it is rational or not, nobody is going to work in a skyscraper if every 20 months one gets knocked over. Just look at Israel and Palestine for what happens to cultures who expect terrorism (on both sides). It is caustic to a free society.

It is hard to tell how low the risk of terrorism is in a vacuum. There are certainly enough suicide bomb volunteers and other jihadists. Crossing the US border is pretty easy.

Some amount of intelligence is needed to make sure nobody is plotting something big.

All that it has bought them is death. Their goal was to take down the US and it tremendously backfired, but we kind of squandered that goodwill. If they want to make money they kidnap Europeans who they know will pay the ransom.

The idea was to get the US to just leave the middle east. And that was a pretty epic failure on Al Qaeda's part. The US is up the middle east's ass a lot further now than then.

Also "they hate us for our freedom" is some dumb Bush era idea. Al Qaeda doesn't hate America for our freedom. Al Qaeda explicitly explained why they hated us. 1) Troops in the Arabian peninsula, 2) support of Israel, 3) blockade of Iraq.

Second, this is an excellent answer.

If the government wants you to give up your civil liberties and uses the threat of a terrorist attack to get you to give them up, then they have become terrorists as well. However, I don't know if that is the explicit goal or not or just the outcome of a grossly over exaggerated response. I do know if someone wants to get their way they usually just say "terrorism" or "children."

Terrorist attacks are rare. Humans are terrible at evaluating risks.

Besides, it's not like "terrorism" is some constant in societies. With the exception of nutjobs, organized terrorism is a response to specific political circumstances and relations between countries. You don't see any terrorism between the Swiss and the French. But there has been between the Irish and the British, for the well known historical reasons. Or in Spain with the Basque countries. Or in the Middle East / Latin American.

It's a political issue, and can be solved at that level, not some natural force that we no other mean to stop except to always be prepared for it, like earthquakes.