In the New York Times today:
“Detention without charge is a regime we don’t want to see,” said Sarah E. Mendelson, a scholar at the Center for Strategic and International Studies who led a study of options for closing Guantánamo. “Having an executive order rather than Congressional legislation is even worse. Then, it’s a continuation of the kind of super power within the executive branch that you saw with the Bush administration.”
...Several human rights advocates met with Mr. Obama and his top advisers before his National Archives speech and warned him that indefinite detention had many of the same flaws as holding prisoners at Guantánamo. “We told him to make sure that the cure doesn’t perpetuate the disease,” said Elisa Massimino, executive director of Human Rights First.
The ACLU today (received by e-mail):
“This is not change – this is more of the same. If President Obama issues an executive order authorizing indefinite detention, he’ll be repeating the same mistakes of George Bush, and his policies will be destined to fail as were his predecessor’s. How justice is served in America should not be an open question in a country where we have a rule of law and a time-tested criminal justice system.
Throwing people into prison without charge, conviction or providing them with a trial is about as un-American as you can get. While President Obama might be experiencing difficulty with Congress when it comes to implementing his decision to close Guantánamo, the answer is not to issue an executive order authorizing a system which is unconstitutional and counter to the most fundamental American values.
....Indefinite detention without charge was unconstitutional under the Bush administration and remains so under the Obama administration, whether authorized by a law or through executive decree. We must put an end to the incorrect and ineffective assumption that the only way to keep us safe is to violate our most basic principles.”
(my emphasis)
This is a not a new position the ACLU is taking with Obama on the issue.
I don't believe that any reputable civil liberties group is advising Obama on the best way to implement indefinite detention -- or expressed a preference for executive order over congressional action. Either is abhorrent and unacceptable.