The CIA refused to interrogate an al Qaeda prisoner who was captured in recent weeks, because the Obama Administration's inconsistent position and likely untrustworthiness in their assurances to the CIA has led the CIA to be so scared of what might happen that they're just washing their hands of it.
This wasn't the emphasis of most of the resistance to releasing the memos, which focused on what our enemies would now know about what the U.S. would be willing to do if they were captured. This problem is on the side of our inability to do anything, apparently. So it seems even those opposing the memo release underestimated how seriously it would harm the effort in fighting against al Qaeda. The president's action didn't logically entail this response, but I think it's surely correct to say that it caused it. This has effectively crippled the CIA, and this particular prisoner may well have dated information that their fear at what Holder's Justice Department might do has led them not to try to get. It also makes me wonder how likely they think conventional interrogations would produce any worthwhile information, because surely they're not scared of doing that.
Update: I guess this argument has been prominently made, but I hadn't see it before. Gen. Michael Hayden, former CIA director and Michael Mukasey, former Attorney General, said in a WSJ op-ed:
Its effect will be to invite the kind of institutional timidity and fear of recrimination that weakened intelligence gathering in the past, and that we came sorely to regret on Sept. 11, 2001.
The rest is well worth reading. Even if I became convinced that this interrogation program was illegal or immoral, I would still think the case against releasing these memos was extremely strong.