What the question is
This analysis by David Paul Kuhn is interesting for many reasons, not the least being the indication that conventional wisdom is shifting enough that it is no longer consider out-of-bounds to publicly suggest that 9/11 could have been prevented.
Of course 9/11 could have been prevented! However, the mere suggestion of that, up until now, would almost assuredly have gotten you labeled a conspiracy kook. But there is nothing conspiratorial about it at all. You don't have to believe that Bush people knew the 9/11 attacks were coming in order to believe that there was sufficient evidence out there that could have been pieced together given a more diligent national security team.
It has always been a question of competence, not malice. It has always been a question of ability, not intentions. The American people owe it to themselves to ask whether a more competent team at the top could have picked up on the hints and prevented a disaster. They owe it to themselves to understand that asking this question does not require you to believe that the Bushies are bad people.
They just aren't very good at their job.