That is mostly correct, but I'd submit that it's because Bush can't express the real reason out loud: that attacking Iraq is part of a broader, longterm strategy to overhaul Islamic culture and politics.
So he's stuck with making the argument in surface or "immediate" terms: Iraq has WMD, Hussein is a tyrant, he has defied UN resolutions, etc.
If the political atmosphere of 2003 actually allowed Bush to say, "Look, fundamental Islamism sucks, and we're going to dismantle it to make sure 9/11 doesn't happen again," there'd be a lot less confusion. Obviously, the political atmosphere in 2003 does not allow those sentiments to be expressed in such a forthright manner.
True enough, but the bully pulpit of the Presidency can be used in many wonderful ways.
Reagan completely undercut press criticism simply by smiling and waving everytime he emerged from the Presidential Helicopter on the White House lawn.
He literally "walked tall" and that image dominated popular thought regardless of the story attached to the footage.
If memory serves, White House advisors were completely opposed to his speech "Mr. Gorbachev, tear down this wall".
It worked and he prevailed.
The Bush Administration,on the other hand, has loosed the hounds of mindless bureaucracy at every airport in the country.
They have endorsed (and signed)legislation antithetical to core American values.
They interfered in local and regional elections in a fashion destructive to the interests of the affected populace.
The medium is the message. By the time the Bush Administration finally acquires it's sea legs the Ship of State could well be sunk.
Best regards,