While I don't see the point in protecting sources that have used the cloak of anonymity to lie in the past, it may be too much to expect the press to change its practice in this regard. For one thing, if protection becomes something the press can withdraw, it could become more difficult for the press to protect sources in cases where protection is needed and deserved. At that point, the press would no longer be saying, "We protect our sources," but, "We think this source deserves protection."
Fortunately, "outing" dishonest sources is not required to encourage honesty among background sources. If a "senior administration official" gives inaccurate background information, that fact could be reported with as much prominence as the original story. If such an official repeatedly gives inaccurate information, they could be described as an "sometimes unreliable senior administration official." If an administration or group has a track record of lying or twisting the truth, anonymous comments can be accompanied by disclaimers reflecting that history: "A senior administration official said that the moon is made of green cheese, but such statements from the administration have proven unreliable in the past."
Today, of course, our news outlets do little or none of this. Not only don't they expose dishonest sources, they don't expose their dishonesty, leaving the strong impression that they're more concerned with currying favor with those in power than in informing the public. As long as that perception persists, it will be difficult to generate public support for reporters such as Judith Miller.