If it was such a slam dunk, why not arrest and prosecute under existing laws? That the federal government felt they needed to take unconstitutional steps undermines their credibility in my eyes.
Does that matter a single iota? Does the US legal system say somewhere you can hold people in prison with no rights because "they sort of are a terrorist, though"?
So what? Even terrorists have a right to a fair trial, and protection from arbitrary detention.
Innocent people should be protected from arbitrary detention, therefore everyone should get a fair trial to determine if it can be proved they are guilty, while they have the ability to defend themselves. An innocent person who is wrongly accused of bombing a kindergarten is just as innocent as a person who is wrongly accused of stealing a candy bar.
On a semi-related note, I hope John Walker Lindh gets a hell of a party upon his release next May.