Those who argue that leaks to the press are never justified, and should always be punished severely, believe that the framers have already put sufficient checks and balances in place so that the system can deal with any situation that could come up without the need for the press to get into the act and sensationalize and publicize the situation prematurely. The proper course of action for a national security employee would be to launch an internal investigation within his/her own agency, and if that fails to remedy the prolem, to go to the committee in Congress charged with Congressional oversight. The legislative branch would be acting in time-honored fashion as a curb on the executive branch, just as the Constitution intended.
Those who disagree with the above base their contention on two ideas: distrust of government oversight (fostered by such events as the initial My Lai coverup, as discussed in Part II), and the public's right to know. In general, they also tend to routinely downplay the security repercussions of disclosures such as the CIA detention centers in Europe (I discuss the origins of this attitude here and here).
The issue is how do you tell when a leak is really a matter of principle versus acting out a political agenda?
There appears to be a simple metric used by the MSM. When the leak hurts the policies of a Republican administration, it is a matter of principle; when it is hurts a Democratic administration it was obviously done out of a political agenda. When a Republican leaks it's BAD and unethical. When a Democrat leaks it's because she is acting from the highest possible ethical (and patriotic) motives.
Perhaps I have become too cynical, but it seems that national security has very little to do with it one way or the other these days.