Matthew Yglesias, noting yet another study that demonstrates the difficulty of correcting lies and myths once they are spread, concludes:
[P]eople who care about honesty ought to consider themselves very seriously obligated to reprimand people who are deliberately spreading misinformation. At the end of the day, it's extremely difficult to actually counter misinformation, and so society needs there to be disincentives to spreading it.
That's a very good point, and something the media does very poorly. Reporters tend to privilege lying, rather than punishing it. In order to remove the incentives for lying, the media should shun, rather than embrace, people who have a history of spreading falsehoods.
To take one obvious recent example: During last year's presidential campaign, John McCain lied. A lot. He lied personally, and he allowed his campaign to lie. A lot. There was actually a brief period when the media acknowledged this; when they debunked his false claims. But then what happened? They quickly moved on, and began rehabilitating him (scroll down to "Rehabbing McCain.) They insisted that wasn't the "real McCain," that he was really "principled" and "honorable." They pretended both campaigns were equally negative. And now? McCain's dishonest campaign is a thing of the past; the media pretends it never happened.
That, quite obviously, rewards lying. The primary disincentive to political figures spreading misinformation is the possibility that they will be seen as dishonest. If the media refuses to make that dishonesty clear, there will be more misinformation.
(Of course, the opposite problem kicks in when the media decides to portray the wrong candidate as dishonest, and make false claims in order to do so...)