I think some of the idea that journalism should be objective comes from the intial radio and TV days. Those broadcasts used, and still use, the public airwaves so they are required and expected to maintain certain standards such as not cussing. Maybe there was a strong push to keep those broadcasts politically neutral so the big hand of government wouldn't give the broadcaster a smack down.
I would say that this. And add the so called fairness doctrine which was in reality anything but fair despite the illusion propagated by the talking heads. Would anyone really claim Russert, Rather, elder Wallace, etc. were really telling in straight down the middle? I always felt there was another side they weren’t telling me. Just logically there should be more to the story ...
As much as I can take or leave people like Limbaugh, we didn’t really hear the other side of the coin until the fairness doctrine was eliminated. Until talk radio and especially the internet came along without the fairness doctrine there wasn’t that dissenting opinion being always being heard. I hate social media, but at the same time now the MSM can’t get away with the one sided stories they did for decades.
And I say this as someone who doesn’t always disagree with the “liberals”. I’m mostly libertarian. I don’t think Reagan was as great as he was portrayed. I hated both Bush’s. McCain and Romney. Well maybe hate is too strong, not a fan let’s say. I voted for Perot twice ... I had disagreements with his platform too, but it wasn’t the regular R vs D or what the media told me to do.