Objectivity in journalism effectively erodes the very foundation on which rests a responsible press. By most any of the many accounts of the history of objectivity in journalism, objective reporting began more as a commercial imperative than as a standard of responsible reporting. There were radical changes in printing technology, including he steam powered press and later the rotary press. There was the formation of the Associated press, an early effort by publishers to monopolise a new technology - in this case the telegraph. These are some of the many conditions that created the climate for objective reporting, a climate best understood in terms of the emergence of a new mass medium and the need for that medium to operate efficiently in the marketplace.
Efficiency is the key term here, for efficiency is the central meaning of objective reporting.
It was efficient for newspapers not to offend readers and advertisers with partisan prose. Metaphor or not, publishers took it quite literally.