One of the scariest thing about terrorism is that it appears to be senseless and irrational. Why would anyone deliberately kill himself by flying into a building? Who could conceivably benefit from killing innocent schoolchildren? Why on earth would Iraqi insurgents deliberately target aid workers that are trying to rebuild their country? Irrational actions are always scary, since they're impossible to predict it and hence prevent.
I think that the 9/11 terrorist acts, and many subsequent ones, are not irrational, when put in the proper context. I think the "war on terror" can be understood as a conflict between memes. For those that haven't hear the term, "memes" are contagious ideas that, like viruses, replicate by passing from mind to mind. The term was coined by Richard Dawkins. Memes can be harmless (like a catchy tune), valuable (like a new scientific technique) or harmful (like the "smoking is cool" meme, which often kills off its host). One key to understanding memes is to view them as independent entities, not just as "ideas". Like viruses, memes can mutate, and like viruses, the memes that spread rapidly and persistently survive the best.
I believe that we are now fighting an extremely wily, dangerous and harmful meme: wily, because it has subverted the minds of its hosts so fully that it has some degree of intelligence; dangerous, because it is fighting for its life; and harmful, both to its hosts and to others. I'll call it RI, for radical Islam, but don't be confused into thinking that I'm talking about a set of countries, or individual people, or even a community of people. I'm talking about a different of creature: an more-or-less living entity that is encoded as set of ideas that propogates like a virus, and that subverts the minds and bodies of its hosts in order to spread and survive.
Let me flesh this idea out more. The first point is that memes compete---particularly memes associated with non-syncretistic religions, like Islam. This means that often memes can have a high level of penetration within an cohesive community, but a much lower level of penetration in the population at large, where they have to compete. (For example, for every guy from Malibu that joins up with the Taliban, there's also a Buddhist, a firewalker, a Wiccan, a Kabalist, an neo-animist, an atheist lawyer, and a physicist working on GUTs.) As societies open---due to economic globalization, cheaper communication and travel, etc---this threatens those memes that require an intellectually isolated community to survive. I believe that RI is such a meme---which is why it is fighting for its life. Western democracy is not (or at least, pre-9/11, was not) actively trying to stamp out RI---but the very existence of a set of strong competing religious memes constitutes a threat.
The second point is that a military confrontation is an extremely effective way to isolate two communities from each other's memes. The heros of the enemy---military or intellectual---become your enemies, and ideas of the enemy become treason. I believe that purpose of 9/11---from the point of view of the RI-meme---was to provoke the west into a military war against the Islamic world, thereby isolating itself from western memes.
Notice that from the point of view of the people in that world, this war might be economically disasterous, and from any military point of view, the war might be unwinnable. But to the RI-meme, the war is helpful, because it insulates it from competition.
So what are the implications of this?
One is that a lot of the current "war on terror" is misdirected. Better security at airports, screening containers shipped into the US, tracking black-market radioactive materials, even cleaning up and policing "failed states"---all of these make some sense as defensive measures. But offensive measures that take the fight to the enemy are not, ultimately, military measures. They need to be attacks on the RI meme, not merely on the society in which its human carriers live.
In fact, as the whole Iraq campaign has shown, conventional military attacks might actually strengthen the RI-meme. The usual military strategy is to attack the enemy's weapons and delivery vehicles, and then his economic infrastructure, making it impossible for him to rebuild. But for the RI-meme, there are no weapons, and the only "infrastructure" it needs is a population filled with hatred and dispair. In fact, economic and social chaos in may actually strengthen the RI-meme, just as weakening your body leaves it vulnerable to infectious disease.
The second implication is that we need to worry about a lot more than simply catching up with terrorists---even if we were 100% successful that would only eliminate part of the infection. We also need to think about prevention---about how to innoculate a population against the RI-meme. I'm not sure how to do this most effectively---for starters, I'd need to understand it a lot better. I'd guess the first thing to do is strengthen the memes most likely to displace it, which are probably more moderate versions of Islam.
Finally, if the RI-meme's purpose is to isolate itself from the west, we need to do what we can to defeat that purpose. We need to do whatever we can to cut through the membrane between "us" and "them". that started forming on 9/11. And we need to do it safely---without subjecting ourselves to additional danger from terrorist attacks, and without inviting PR fiascos that lead to more hatred against the west, and without unnecessary conflicts that lead to further isolation.