You mean, worse than the destruction of Iraq, the draining of the US economy, the shredding of civil rights at home and abroad or the ruination of America's reputation around the world?
But I guess you could argue that all those things would have happened without 9/11, since it's now an open secret that Bush already had plans in place to be a "war president" and would have found some other pretext if Bin Laden hadn't obliged.