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No doubt many influential bloggers do not reveal their identities for various reasons. But their work, for all the public to see and evaluate, is their true measure.
Glenn has worked with Anonymous Liberal* in the past. Now, I don't know if AI is "out" or not, but it doesn't matter. The views expressed by the "out" Glenn and the "in" AI don't require that we know their true identity. They are not using some secret information they obtained surreptiously, but they are utilizing newspaper accounts, etc. to analyze and break-down the malfeasance of this administration and others.
Neither Glenn nor AI (and all the others) are acting as a modern-day Deep Throat or whistle blower. Their identities are irrelevant.
*I don't really know if AI is anonymous, just using him as reference point.