There are many possible reasons for declaring something secret. The example I usually use is the Queen of England's panties. Were a diplomatic post to state that on this day the Queen was wearing white silk panties with a repeating pattern of gold tiaras, that would seem to be a stupid thing to classify top secret but, I'm pretty sure that it would be. The reasons are that it would not be good for the relationship of our nations if the British found out we were spying on them. And, it would start a hunt for the source of the information. If it were humint, their freedom certainly and possibly their life would be in danger. Finally, it would be a leverage point for other actors to use, a potential for blackmail if you will. Sometimes it is simply a matter of timing. If something classified is in the newspaper a day, or even several hours later, we might still want it classified so as to protect the information that we had the information prior to it being public. Again, lives could be endangered if it is known that we knew hours before. It has nothing to do with the rights laid out in the Constitution and everything to do with the hugely complex day-to-day interactions with hundreds of other governments and non-governmental entities.

To attempt to downplay the complexity of governmental interaction is the republican ploy. The truth is, it doesn't all fit on a bumper sticker. We could and should take steps to minimize the amount of classified information but, I'm not sure how that might work. If you can convince everyone else in the world to be completely open and honest, I will certainly support that behavior of our own statespeople.

I'm thinking martyr in the sense of "prisoner of conscience."

If imprisoned, he won't see the light of day again and there will probably be extraordinary measures taken to cut him off from human contact.

IOW, they may as well kill him.

ETA:

There is nothing in the Constitution that give the government the RIGHT to act secretly and hide everything that it does from its citizens.

But, but, but... [Tevye] Tradition! [/Tevye] Traditionally, the state has been "empowered" to keep "state secrets" in the interest of "national security."

(That our notion of national security often means that we covertly interfere with the conduct of a sovereign state's internal affairs, a/k/a their national security, is one of those bitter ironies that has long been understood by people who've been paying routine attention to such matters for years. Again, "no shit." But still, when these memos come to light, the roaches go running. I'm still surprised that the Suharto and Pinochet memos were allowed to surface with Kissinger still out metabolizing oxygen.)