I think there are some general guidelines that the U.S. as a society could follow to avoid terrorism. Unfortunately these will be rather to difficult to do in practice.
* Invest heavily in intelligence to find out what people are doing.
Spies and double agents seem to be the best sort of intelligence. Unfortunately they are put into very dangerous situations, which means that morally they must be restricted to only volunteers.
Surveillance technology is also an important part of this. Given the threat, I do believe that it is appropriate for the government to automatically tap everybody’s phone calls. However, in order to maintain our society, it is essential that that the dissemenation of this information be tightly restricted. In particular it must not be used in any court case or legal action which does not involve terrorism. History shows us that this is a very difficult restriction for the government to follow. Legal tools devised to combat terrorism are quickly perverted to use against organized crime and drugs. This is not acceptable.
Surveillance technology should not be oversold: it has historically not been useful in protecting against a threat. However, it also should not be undersold: it has been extremely useful in rapidly determining what happened. Dealing with terrorism must consider reaction as well as prevention.
* Invest heavily in tracking and control of dangerous radioactive and biological materials.
This is really a no-brainer. We should invest heavily in safely decomissioning existing radioactive materials including that in the former Soviet Union. We should try to track it whereever possible.
It is much harder to track biological materials, but we should do what we can.
* Don’t give people a reason to attack us.
This is the hardest one to implement. History shows us that suicide attacks, which are obviously the ones which are hardest to stop, are normally used against people who are perceived to be occupiers, and are not normally used against people who are in other countries. Osama bin Laden considered the U.S. forces in Saudi Arabia to be an occupation. And, indeed, we did move our forces out not long after 9/11. So: to avoid extreme forms of terrorism, don’t occupy other people’s countries. Duh.
Unfortunately our energy infrastructure requires us in some cases to use military force to ensure continued supply. This is a terrible idea on many levels. Our highest priority as a society should be to change this. There is unfortunately no single clear fix, but there are many competing solutions which may help. They should all be followed in parallel.
There is also the problem of Israel which is, to say the least, fraught with complexity. Israel is an ally which deserves our support. However, Israel is also perceived as an occupying force. While I know this is a touchy subject, I think that, especially given that many people still alive were born before Israel was created, it’s very difficult to argue that this perception is incorrect.
I think we should stop supplying arms to Israel. But we must not abandon the country militarily: I think we should deploy a permanent force in the Mediterranean to support the country if it is attacked. This will be expensive but not absurdly so by the standards of our defense budget. I think we should strongly support the Palestinians, which means investing to create jobs, a civil society, and a real nation. Israel and Palestine will never be easy neighbors. But I believe that it is possible to get them to the point of fighting with words rather than guns. I believe these steps will remove a huge incentive for people to attack us.
(As a side note, it is amazing to me that the Palestinians have not tried wide-spread non-violent resistance. Given the nature of Israel, a Palestinian Gandhi would be enormously effective.)
* Continue the reactive security theatre where reasonable.
By security theatre I mean the invasive searches required when boarding an airplane, the checking of IDs when entering goverment buildings, and the general climate of fear induced by the current administration. These things are almost completely useless against determined terrorists, and would have done nothing to prevent 9/11 in particular.
But they do address another serious problem, which is the random nutcase, or, to use John Brunner’s word, muckers. Muckers are the people who shoot up schools, blow up federal buildings in Oklahoma, set their shoes on fire on an airplane. They can not be controlled by the above approaches. But they are also neither highly intelligent nor well organized. While the security theatre does have a political goal of impressing ordinary citizens, it does also play an important role in preventing random attacks. On that basis it makes perfect sense for security theatre to be reactive: the muckers are more likely to repeat existing ideas than they are to come up with their own new ideas.
Finally, I want to note that despite all we do to prevent terrorism, the issue of random unprovoked violence is only going to get worse. The Industrial Revolution has steadily increased the amount of destructive power which an individual can wield. That trend isn’t slowing down. If you think things are bad now, wait until hand held rocket launchers get out of the hands of quasi-organized militias into the hands of the muckers. Then wait for the suitcase nuke to follow the same trend–although hopefully that will take another hundred years.