Concerning WikiLeaks
Listening to discussions of the case, one repeated theme is that there are some things the government should be allowed to keep secret. That is not an unreasonable view, but I do not think it has much to do with the case. If the government had kept its cables secret, they would never have reached WikiLeaks.
The question at this point is whether when the government fails to keep something secret, when it gives access to its secrets to someone who proceeds to pass them on, it is entitled to put the genie back in the bottle by making everyone whom they have been passed on to, at least everyone with the ability to publicize them, shut up.
Legally speaking, the answer is that they are not—as in the case of the Pentagon Papers. I think that's the right answer. If keeping things secret is important, the government should keep them secret, not let them out and then do its best to gag the press in order to keep the general public from learning them.
Instead, as best I can tell by public discussions, the U.S. government labels a wide range of things secret and then lets a wide range of people have access to them.