It seems perfectly plausible to me that releasing video of the Pentagon being struck by terrorists would only serve to glorify the events that day. At the end of the day those agencies did their job and secured any footage. This gave the government the opportunity to decide what is released to the public and I think they made the right choice considering the promotional value of it to the terrorists.
That's not how this works. Classified material is not classified because it would make people feel some type of way. It's because the release of the material would have some effect on national security. With the end of the war in Afghanistan, there is no clear reason in my mind why the declassification of any existing video would be a cause of concern.
"National Security" as a term is broad enough to include anything. Case on point I see "national security" given as a reason why economic espionage is okay or why the government won't release things that are embarrassing to politicians because it can effect how foreign leaders view them and that's "national security".
