Since this question has been posted on Edge. I've been casting around for something useful I could say something that I could recommend we do. I've failed. Most of the techno-fix and cultural solutions that occurred to me were either unworkable or simply closing one of many stable doors after the horse has bolted. So instead I've decided what to do at a personal level: as my tiny contribution to this learning experience I am going to become less tolerant.
A lot of people have expressed the opinion that we need to become more tolerant, not less; that we need to understand the reasons behind the terrorists' actions and see how their decision made perfect sense to them in the context in which they found themselves. Speaking for the human species as a whole I think this is true, but for myself I would say that I have always thought this way and have probably been overdoing it. I'm a "cybernetic" fatalist: I consider that most people, most of the time, find themselves in situations where they have no real choice. Murderers do not kill on a whim, and governments do not start wars for amusement. They do it because their circumstances have driven them to it, or at least because they believe their circumstances have driven them to it, which is essentially the same thing.
All complex systems, from brains to societies, contain myriad feedback loops. Every now and then something will happen that triggers the creation or dominance of a positive feedback loop, which drives the system into some extreme state. From here it will probably rebound and thrash violently, eventually perhaps shaking itself to bits. Once started, these things become increasingly hard to stop, and beyond a certain point the individual actors in the drama will be impotent puppets, driven to do whatever they are driven to do, regardless of how distasteful they find it. So from my position as a cyberneticist I have always been (I hope) extremely tolerant of people when they act as they inevitably will in the context in which they find themselves. By the time someone does something truly awful it is probably fair to say that it's not their fault.
Nevertheless, the purpose of intelligence is precisely to predict such runaway situations well in advance and prevent them while we still have the energy to do so. Only the stupid blunder into situations from which they have insufficient power to extricate themselves, and at the level of individual organisms it is this predictive energy management that keeps us alive. Equally, it is our responsibility as members of the human race to ensure that we do not do things that might let the whole of society run out of control. And we already know a good deal about the science behind such systems behaviour. Blame does not, therefore, lie with the end product the terrorists, murderers, hooligans and bullies. It lies with those of us who make trivial decisions with insufficient thought as to their long-term consequences. The terror starts with a poorly considered policy, a minor bit of selfishness or a moment's lapse of concentration. Above all it starts with simplistic, fallacious or lazy reasoning.
Perhaps the clearest sign of a lack of intelligence is the inability to distinguish more than two categories at once. For such people the world is divided into Us and Them, Black and White, Good and Bad, while in reality nothing is that simple. Such people frequently lapse into dogma, and I agree with Richard Dawkins about the culpability of religion in this instance (on both sides the number of times God was invoked by Westerners in the aftermath of this tragedy depressed me enormously). Religion is a powerful force for polarisation, as are nationalism, sexism and party politics. Such dogmas create monolithic and potent forces that can easily topple the system. They allow people to be lazy; to avoid taking personal responsibility and ally themselves blindly and unquestioningly to a formula (whether the Bible, the Koran or a manifesto).
What we need is for all of us to use our brains to the best of our ability, and when we see lazy, selfish, illogical or short-term thinking in other people, we should point it out to them in no uncertain terms. So I have vowed to become less tolerant of stupidity and irresponsibility than I have been. From now on I intend to be militantly intellectual. I shall always remember my moral duty not to hurt people's feelings, but their beliefs, cultural assumptions and political opinions I shall consider it my responsibility to consider and then, if necessary, to challenge. Sadly, it won't save anybody's life today, but it may help avert disaster for tomorrow.