Security: impossible to accomplish

We've all seen the horrifying images of September 11th, and wondered if we are ever going to be safe again. The problem is that we can't be safe because we never expect an attack like this but now that we can imagine any form of attack, can we be safe? The answer is a definite NO.
We can never be completely safe for acts of terrorism and attacks are no longer precipitated by nations but by the ideological groups that conduct their operations within them. We aren't playing the domino theory anymore where if one country falls under a certain belief that we should move to contain it or risk losing others. These ideological groups like Al-Qaeda, the Tamil Tigers, Hezbollah, etc. act more like parasites (not in a derogatory way) but that they are free to conduct operations in any given country and even if one country catches them, a separate branch of that group takes over. The Cold war is another example for we imagined a possible invasion by the Soviet Union and even came close to a nuclear war with them during the Cuban missile Crisis. Another example would be the Maginot Line in France. After the first world war, France knew that Germany would inevitably rearm and rather than risk another bloody Western Front, they built a series of fortifications along the German-French border. They did not imagine the possibility of the Germans launching full scale assaults through Belgium and the Ardennes forests until it was too late.
Finally, we can't be safe because security has a certain scale of when too much has been added. I speak of course of George Orwell's famous 1984 scenario where security and governmental control is strong but liberty is extinct. That's why public opinion polls in New York City opposed the installment of security cameras throughout Central Park as the people would feel uncomfortable with security forces watching them all the time. There lies the tragedy, security is actually judged by the various opinions of the public not by some traffic light-like chart that indicates when the US is safe and when it is not. They want to feel secure yet not too secure. Sounds too much like the Goldilocks story. So when will Americans feel that security is "just right"?