Eugene Volokh and my friend Mark Kleiman both express doubts whether a journalist who had received information from a confidential source would honor a waiver that had been obtained in the manner I had suggested. Their premise seems to be that the journalist would view such a waiver as illegitimate because it was "coerced." Let me make a somewhat finer distinction.
It appears to me that there are basically four types of confidential communications made to journalists by public officials. The case for honoring the product of a "mass waiver" in some of these cases is stronger than in others. I think that the Plame case involves the strongest case for arguing that the journalist should honor the waiver.
At one end of the spectrum, there is the "Deep Throat" disclosure. That is, a disclosure by a confidential source who is, in essence, blowing the whistle on wrongdoing inside of an administration or an agency or department thereof. I can understand why a journalist would not honor a "mass waiver" in this case, since it would be tantamount to allowing the fox to silence the squawking chicken. In the Watergate context, for instance, had there been a "mass waiver" and the waiver were honored, the truth may never have come out.
Closely related to the Deep Throat type of revelation is the "intramural" leak. That is, officials in one area of the administration (e.g.the State Department) releasing information in order to gain some advantage on a bureaucratic rival (e.g.the Defense Department). I'm not certain whether, as a general question of journalistic ethics, such a "mass waiver" should be honored. However, it is unlikely that an administration would likely ever seek such consents in these circumstances, since to do so would be to demand a public airing of its own dirty linen.
In a similar fashion, the third type of confidential disclosure will likely never be the object of a "mass waiver" directive. This disclosure is the "background" disclosure where officials, whose identities are actually known by all of the policy players, make disclosures either to float trial balloons or to give an "unofficial" warning of some kind that would be too harsh or pointed if the identity of the party making the disclosure was known. Such disclosures are common, and indeed accepted, in the foreign policy arena. It is unlikely that there would ever be an organized push by an administration to make the source public.
Finally, we come to the Plame case. Here, the confidential source(s) were presumably seeking to advance the policies of the administration that they served. However, the offense and the reason that disclosure is sought is that the nature of their disclosure was truly a "foul" (and, of course, may actually have been criminal), intended to harm Wilson and his wife. I think that a "mass consent" should be honored here because the consent is elicited by the organization, that is, the Bush Administration, that was the intended beneficiary of the leak in the first instance. By forcing the leaker to identify himself or herself, the Administration would be disclaiming any relationship to the leak, painting it as a true rogue operation. Under such circumstances, a consent, even though the product of some degree of coercion, should be honored, since the disclosure can no longer be seen as advancing the any legitimate policy interest. With the underlying rationale for the disclosure removed, the disclosure becomes a sort of bare personal assault against Wilson and Plame. Under such circumstances, the source cannot legitimately demand protection. In other words, once the disclosure has become delegitimatized as a tactic to advance some broader public policy goal, a journalist should feel no compulsion to honor the confidentiality pledge.
It is becoming painfully obvious that no consent along the lines that I have outlined will be sought by the Bush Administration because, at some level, the Plame disclosures are still viewed as legitimate tactics to be used in support of the Administration's policies.