What human related event, when recorded in any way by person or technology, is unaffected by bias or subjectivity? History is written by the winners indeed.
I enjoy the multitude of news/media sources available to me, and I take responsibility for employing my own filter. There is an off button on my computer and TV as well.
I don't disagree with anything you say. I'll reiterate, though, that when people get in heated debates about whether corporate media overall has a liberal or conservative bias they are unaware of the broader picture. There is also a difference between different biases, such as liberal or conservative, or by historians with a plethora of different perspectives, and conforming, unidirectional bias.
On a related note, the first president to get 80% approval for anything was FDR, shortly after mass media came into full fruition (something not lost on Hitler). Whether FDR (or Bush II) should ultimately be judged right or wrong for their corresponding decisions that gathered overwhelming support, neither enjoys the level of support they received without mass media. Such media has gone from increasingly independent and decentralized to consolidated and corporate, particularly from the seventies on. This trend has concerned both conservatives and liberals, by the way, though an independent and much diffused Internet now stands as the hopeful way out.