The mentality behind the MSM? Selfishness, pure and simple. Selfishness and cowardice.Cheap talk about how bad everyone is who has to make decisions and live with the results - who have to work to a bottom line - makes journalists feel superior to the people who make the country work. That is pure selfishness.
The MSM coheres in the idea that nothing actually matters except PR, and each individual component of the MSM gets good PR from all the others. Provided, of course, that the favor remains mutual. But the moment any person or institution ceases to support the pretensions of any of the others, all of the others will turn on him and drum him out of "objective journalism."
So the MSM is at bottom a mutual admiration society and a non-aggression pact which makes the MSM cohere in selfishness and fear. It is united for the purpose of picking on people who are natural Republicans - people who have responsibilities and who naturally make mistakes because they actually do things.
The result is that the MSM is hyper partisan under its facade of "objectivity"; liberal politicians do not so much lead and direct the MSM as they follow it, and operate in symbiosis with it.
Why Broadcast Journalism is
Unnecessary and Illegitimate
You use the media as your focus but you are basically describing human nature, or at least a particular embodiment of it.