(via Instapundit)   Brink Lindsey has this OpEd in National Review on-line describing how Al-Qaeda-esque terror is just the latest bout in the eternal struggle between civilization and barbarism:

Here is the gist of it: We find ourselves, once more, in that paradoxical vulnerability that our forebears suffered for more than 20 centuries. The old menace, long vanquished, has returned in new guise. We are threatened again by an enemy whose weaknesses in peace become strengths in war. Our civilization is exposed to ruin by the very sources of its greatness. After a long respite, the barbarians are at the gate again.

Brink echoes a favorite Rumsfield quote of mine --  "our enemies attack things they can't build themselves using weapons they can't build themselves."   They are unable to domestically create the fabulously complex, socio-economic machine necessary to build a 757.  Or make a World Trade Center financially viable.  But this inability also gives them the formlessness to evade a full military frontal assault upon their "factory".  

Stylistically, Brink seems to have lifted a page or two from Victor Davis Hanson and laces his article with historical examples  ;-).  He concludes:

...We face, now and for the foreseeable future, the threat of a new barbarism. The new barbarians, like those of old, consist of groups in which every member is a potential warrior. Like their predecessors, the new barbarians rely on their ability to outmaneuver their civilized adversaries, to concentrate deadly force at vulnerable spots. But unlike the old steppe nomads, the new barbarians seek neither booty nor conquest. Our new barbarian adversaries pursue a strategy of pure and perfect nihilism: They seek destruction for destruction's sake. Their strategy, in other words, is terrorism.

Well said.  And herein lies the heart of the preemption argument.   You can only deter an enemy if their destructive acts/aggression are being used to secure some positive good for themselves.   Deterrence, at its heart is the plausible denial of spoils to the aggressor.   When dramatic acts of carnage are their own goal, the only solution available is preemption.