Why is Jose Padilla so dangerous
That he was denied a trial ?

It has long been clear that he was not such a threat to US national security that the constitution had to be sacrificed to stop him. He is no Jefferson Davis, of course Ashcroft wouldn't consider Jefferson Davis an enemy combatant in spite of the fact that he technically lead a war against the USA.

The problem seems to be that once one decides to ignore the law, it is very hard to stop. This is revealed by the New York Times today
"In the end, administration officials considered Mr. Zubaydah's interrogation an example of the successful use of harsh interrogation techniques.

... he ... was the source of information about Jose Padilla,"

This would tend to make it a bit difficult to put Padilla on trial. First because evidence obtained by torture would be inadmissable, and second, because Padilla's defence team could have learned that the US government was using torture.
Ashcroft et al, with their contempt for the wall between national security and criminal investigations, must have refused absolutely to consider how illegal techniches inevitably propagate when one has to cover up one breach of the law with another.

In this case, the fruit of the poisoned tree was a direct assault on the US constitution.