I am old enough to remember when the media was not graded like fruit coming through a packing plant where the oranges are graded and sorted by color and size. Media was media. Beginning with the era when the John Birch Society occupied the space in society now occupied by The Tea Party Folks. They began accusing media they disliked of being liberal... when most of the population didn't understand what conservative and liberal meant as a political terminology.
So once the labels were tagged onto certain media and certain journalist, whether the tagging process was accurate or not, we began developing this internal detector mechanism by which we all today grade all media content into good and bad.... whether we have the brain power to do so accurately or not.
Back in the 1930s through the 1960s, liberal and conservative were not everyday terms in our national conversation the way it is today.
I was the News Director and reporter for a well known little midwestern radio station in the 1960s, and in my conversations with a very, very involved station owner, I don't thing the words CONSERVAITVE and LIBERAL ever came up a single time during my tenure.