Journalism's obligation to truth

An interesting opinion piece ran in the New York Times today, from the public editor, Arthur Brisbane. He asked "Should the Times Be a Truth Vigilante?" and raised questions about journalism's - and journalists' - obligation to telling the truth - even if it means challenging the assertions of the very people about whom they are writing. He wonders,

"An op-ed columnist...has the freedom to call out what he thinks is a lie. My question for readers is: should news reporters do the same?"

He also wonders if it's possible to be fair or objective in a situation in which a journalist may "choose to correct one fact over another."

These are important questions, and ones that are especially tricky in the world of environment, science, and natural resource journalism. To all of our alumni out there: I wonder how you grapple with these concerns, and how do you strive, to the best of your ability, to tell the truth? What confounding factors get in the way? Does it ever seem that there is more than one "truth," or more than one reality, buried within an environmental story? How do you get to the bottom of these complicated stories?