A philosophical question: Should journalists knock down stories that are either false or substantially misreported in other media?

This question comes up constantly, and I think there are convincing arguments on both sides. I have long agreed that at a certain point, responsible journalists need to step in and knock down rumors for which no reliable evidence exists.

Two of the more prominent recent examples: The "controversy" over President Barack Obama's birth certificate, or the "question" championed by Andrew Sullivan about whether Sarah Palin was really pregnant with baby Trig.

People who believe in these things seem to forget one of the cardinal rules of journalism: It's an extremely competitive field. If there really were compelling evidence that elections had been fixed on a massive scale or that a sitting president committed a crime, documenting the story would earn the reporter who broke it worldwide acclaim and a lucrative future.

So if nobody in the literally thousands of credible news outlets out there accomplishes that, shouldn't that be a clue that the "evidence" doesn't stand up to scrutiny?

Of course, there's another side to that coin. Sometimes an incident doesn't check out, but it's not important or widely known enough to merit a knockdown story. In those 'tweener cases, I see the wisdom of simply not reporting on them, so as not to get the inaccurate or exaggerated information to a larger audience in the first place. Each situation has to be judged on its own merits.