Judith Miller, the finest reporter over there at the New York Times, sits in jail, even as we speak, for reasons that are so obscure that I still can’t figure it out. The essential fact is that a federal grand jury demanded that she reveal the name of a confidential source, and standing on her First Amendment rights, she refused. True grit!
Maybe some emphasis will answer the writer's first phrase. The First Amendment includes no right to refuse to answer the questions of a grand jury. All you have is the Fifth against self-incrimination (until 5 SCOTUS justices decide differently).
I'm not disagreeing with you, exactly, just pointing out that it's not that clear-cut. The law has always accepted the notion of privileged communications -- spousal, priest-penitent, doctor-patient, lawyer-client --on the principle that society benefits from those protections more than it suffers from the impediment to investigating crimes.
The argument in favor of a "reporter's privilege" isn't inventing a new legal theory; it's just arguing that the job of a reporter is similarly situated with those of priests, doctors and lawyers, in that they can't do the job if they can't ensure candor by protecting anonymity. That argument presupposes that the job is worth doing, and that society benefits in some way the law should protect.
Is protecting confidential sources an inherent part of freedom of the press, necessary for it to do its work? SCOTUS ruled 5-4 that it isn't. But 31 (at the low end; the number varies in various sources) state legislatures thought it was, and passed shield laws, so it can't be dismissed as a fringe notion.