Unlike most commenters, I think Greenwald is giving very evasive answers to perfectly legitimate questions. Any operational details about the NSA could plausibly be useful those who are trying to evade surveillance. To me the correct answer is that yes, some details could help terrorists, but only minimally so, and that needs to be balanced against the right of citizens in a democracy to understand what their government is doing. Instead, Greenwald stakes out a completely untenable position that "not one line...could even possibly be said to damage national security."

After he says this, the interviewer brings up the specific detail of metadata collection. Now maybe knowledge that the NSA uses metadata will have little impact on terrorist operations or maybe it will have a lot, or maybe none. I don't know. But if I wanted to know, I'd ask someone who had "very carefully" thought about the national security implications of that publication. Instead, that person changes the subject to other surveillance tools and then says that of course terrorists knew they were being monitored, but with no mention of metadata. That's it? I'd certainly hope that the very careful consideration of national security was more thoughtful than that answer.

It's obvious that Greenwald would rather talk about privacy than national security implications, but even he admits that national security is relevant with his "not one line" comment. He can't have it both ways by claiming that there's no harm to national security, but then treating any question for details as an insult. I see on Wikipedia that he complained that this interview focused "almost entirely on the process questions" but I see that as a natural course for the interviewer to take given his refusal to answer such questions.