I'm trying to figure out WHEN this was the original job, and when it changed. My pessimistic theory is that it has always been talked about, and always been corrupted. But I could be wrong.
When cable news came out and the nation stopped receiving its news one man anchoring the "national" nightly news, just like he has since your parents were your age.
When it's up to Walter Cronkite to report the news to everyone, he has to uphold "journalistic integrity" so that there isn't a personal backlash against him...forcing the network to find a replacement or lose half their ad revenue and viewers.
When nearly every person in the country gets their news from a single source, his integrity as a PERSON is on the line to report the news without bias. When he paints a biased picture, it reflects poorly on him. He becomes a person who lied to the nation for his own selfish agenda.
When cable news came out and people stopped getting their news from a single guy that they grew up watching every night, all that changed. When cable news lies, it isn't a "person" who's betraying you for a selfish agenda, it's some nameless corporate conglomerate feeding you garbage...which you expect from faceless business entities. And since news really happened, some version of it must be the truth...so when that agenda falls in line with YOUR personal agenda...then it's the "true" version of news. The ones telling lies are those hacks at the OTHER news network.
When you're no longer responsible for giving impartial information to EVERYONE, you are suddenly responsible for getting ANYONE to come to you for their news.
If you remain impartial, you become boring...and people leave your broadcast for the one that gives them the news the way they want to hear it.
When Ron Burgundy was replaced by false youtube video preview screen cap promises of anchorwomen holding open their blouses...journalistic integrity went bye-bye.