You can believe that if you want. I don't. It's a myth that such a duty exists. Unicorn-level myth.
There is the libel-untruth barrier, to be sure. And on paper, incitement to violence barrier, although plenty of writings advocate violence and the government doesn't prosecute.
Taking for the sake of argument such a duty exists, is the press meeting its duty? And if not, what are the consequences (to the media, not to the dupes who believe).
However the duty remans, and it should be the primary--perhaps the only--objective of those controlling the media.
Whether or not they intend to rise to this duty, or want to rise to it, or laws require them to rise to it are all beside the point.
The duty of the free press to inform the public truthfully is as self-evident as the fact that governments derive their just powers from the consent of the governed.