[OneWingedShark]

It lets the government indefinitely detain people it deems to have “substantially supported” al Qaeda, the Taliban or “associated forces.”

The problem is that implicit in the action is the guilt:
That is to say that the detention under the accusation [of Al Queda or Taliban association or support] prevents challenging the accusation.

In essence, this is an end-run around the 6th amendment:

Amendment VI
In all criminal prosecutions, the accused shall enjoy the right […] to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; […]

There is no way to challenge the veracity of the charge and because its detention rather than prosecution they hold that it's all perfectly legit.

[Jim Robinson]

The NAZIs were working legally and totally within the law at the time and their actions upheld by the courts.

Unless based on God’s law, the rule of law and the courts are pretty much meaningless.