Despite all the ominous warnings of wily terrorists and imminent attacks, there has been neither a successful strike nor a close call in the United States since 9/11. The reasonable -- but rarely heard -- explanation is that there are no terrorists within the United States, and few have the means or the inclination to strike from abroad.
It is worth remembering that the total number of people killed since 9/11 by al Qaeda or al Qaedalike operatives outside of Afghanistan and Iraq is not much higher than the number who drown in bathtubs in the United States in a single year.
Although it remains heretical to say so, the evidence so far suggests that fears of the omnipotent terrorist may have been overblown, the threat presented within the United States by al Qaeda greatly exaggerated. The massive and expensive homeland security apparatus erected since 9/11 may be persecuting some, spying on many, inconveniencing most, and taxing all to defend the United States against an enemy that scarcely exists.
I think this article is too quick to dismiss in the impact that the invasion of Afghanistan had on Al'Queda, but the general thrust doesn't require this observation to be acceptable.