What 911 really did was shift the counter-terrorism argument from, "we have to cope with the terrorists," to, "we have to deal with them." Even before 911, Islamic radicals with long memories tried to warn Osama not to mess with the Westerners, because they will eventually mess you back, big time. The black bird is on Osama's back for now.
But many people, especially outside the United States, are trying to convince America to go along with the more popular "coping with terrorism" approach, rather than chasing after the bad guys with military forces. That's because this approach could, according to many non-Americans, create more "Black Swans". But counter-terrorism experts in the United States disagree with this more passive approach, because they fear that, without the pressure provided by the invasions of Iraq and Afghanistan, the Islamic terrorists would come up with more "Black Swans". No one is sure which approach is right, and the loser here will get a "Black Swan" as an unwelcome prize.
[The "black swan" is the unanticipated event that our Pentagon is trying to anticipate.]
The heart of the difference is whether we cope with attacks, hoping our enemies don't hurt us too badly, and hoping our enemies tire of attacking us on the assumption that if we don't provide reasons for them to attack us they won't come up with excuses of their own; or attempt to stop the attacks by killing the enemy and actively discouraging them before they really hurt us badly. The assumption of the latter approach is that our acts or non-actions are merely excuses to kill us.
On the latter side there is also a division over whether we should fight this as a narrowly focused battle against jihadis or whether we need to reform Islam to keep it from sending out jihadis.
This is at least a useful debate to have instead of the vile accusations masqerading as a debate that Bush lied us into war. I wonder what our Left wants to have? A debate about our national security or a Bush-bashing therapy session?