It's a well thought out essay. He makes some excellent points that are generally overlooked. (Though I must say, the thickness of my skin was tested. Thank goodness for that good-old, American, pragmatic self - correction. ;-)
I would argue with this point:
Pace John Quincy Adams, America is now precisely going abroad ‘in search of monsters to destroy’.
What motivated our search? It was not something we began on our own, simply because we had too much power and time on our hands. The monsters came looking for us, first. And wouldn't that be the qualifying factor which keeps us in agreement with Adam's original thought?
As for this:
they have re-energised America’s sense of mission very, very powerfully. It is expressed in universal, unlimited terms, not just as destroying the perpetrators of the acts of September 11
Do they actually believe we should simply wait around for a major terrorist attack with death tolls in the thousands, perpetrated by each and every terrorist organization, just so we can satisfy their elusive idea of moral justification? I would argue that we waited too long after previous attacks on our country (USS Cole, etc) and very well may have been able to save some lives by more decisive actions via an earlier "search".
He certainly ends his argument weakly, imo.
...by emphasising her military dominance, by requiring her to use her vast power conspicuously, by making restraint and moderation virtually impossible, and by making unilateralism an increasing feature of American behavior—is bound to generate widespread and increased criticism and hostility towards her. That may turn out to be the real tragedy of September 11.
In proposing that the real tragedy of September 11 could ever possibly be critisism and hostility from Europe (and I have to assume by the author himself?) I would say that qualifies them to join us in the "...brashly and complacently self-confident, over addicted to self promotion and boasting, ‘full of themselves’ as we would say." catagory.