Controlling or manipulating public opinion has always been the objective of the media. Sometimes the manipulation is honest, sometimes it is not. It certainly has no duty to the truth, other than not crossing the libel line. On the truth side, they can be punished for disclosing military or cryptogtraphy or government snoop capability and practices.
The press created the "duty to truth telling" ethical myth in order to increase its power to maniupulate. Who'd believe a press that said "we lie when we feel like it"? LOL. Of course they claim to be pure as snow.
The duty—in fact the only duty—of the news media is to inform the public truthfully.