Opponents of the Iraq War bizarrely continue to argue that the war is and always was unjustified because President Bush was wrong that Saddam had something to do with 9/11.
That would be a fascinating debate to have if the President ever asserted that.
There is little to indicate that Saddam ordered or directly assisted 9/11. I don't think he bears that responsibility (though I would not be terribly shocked if information came out that showed Saddam did have a role).
There is, however, plenty of information that shows Saddam supported and hosted al Qaeda.
Saddam's Iraq was a threat to us and we were justified in taking out Saddam's regime.
Amazingly, just as war opponents deny Saddam's ties to al Qaeda and his threat to us from developing WMD, the permanent pacifist class denies any threat from Iran.