Why journalists should burn dishonest sources
Journalists have a duty to expose anonymous sources who knowingly deceive them. Anonymity is a quid pro quo, and ethical journalists only offer it in exchange for valuable information that they can't get any other way.
The promise of anonymity shouldn't be absolute. Anonymous sourcing sacrifices some transparency for the sake of important information. A source who knowingly peddles forgeries under the cover of anonymity is abusing the reporter's trust and the trust of his or her readers. That kind of behavior must have consequences.
The best remedy is to reveal the identity of the person who passed off the fraudulent information in bad faith. The only reason we tolerate anonymous sources is to get good information. By practicing deception under the cover of anonymity, dishonest informants thereby undermine whatever justification the reporter had for granting anonymity in the first place.
The public has a right to know who's shopping bogus stories to the press. We also have a right to know who duped the reporter in question. Granting anonymity is a journalistic judgement call. When a source turns out to be a fraud, we need to know who that source was so that we can assess whether the journalist granted anonymity responsibly. If it turns out that the reporter has been granting anonymity frivolously, or to blatantly untrustworthy sources, he or she shouldn't be allowed to simply blame the anonymous source and move on.
For example, it makes a big difference who Jason Zengerle of the New Republic was dealing with. If we don't know the identity of the informant who forwarded Zengerle the partially fabricated email, we have no way of knowing whether Zengerle was honestly duped or whether he was using anonymity to conceal the dubious quality of his source.
The policy of burning deliberately deceptive anonymous sources should be enforced at the editorial level. Once deception and bad faith have been established, it shouldn't be the reporter's decision. If, after consulting with the reporter, an editor is convinced that a source was deliberately deceptive, the source's identity should be revealed as a matter of institutional policy.
Anonymous sourcing is a necessary evil. Enforcing consequences for those who abuse a reporter's trust will improve the quality of anonymous sourcing overall.