A few years ago, I had read Bernard Goldberg's books "Bias", and "Arrogance", both of which were critical of the liberal bias of mainstream media. And Goldberg's books and examples were absolutely convincing.
Today, I just completed David Brock's "The Republican Noise Machine: Right-Wing Media and How it Corrupts Democracy" which takes the opposite view, and is critical of the conservative bias of most talk radio and TV cable shows. He shows how the conservative media, which he had previously been part of, have intimidated members of the mainstream, and in order to not appear biased, have moved the political center much more to the right. His book and examples, like Goldberg's, were also very convincing.
The take from this is, like beauty, bias is in the eyes of the beholder. Brock gives many examples of what was mis-classified as liberal bias in his book. In his examples, it's difficult to see how rational people would consider those examples to have been classified as being biased toward the left. He also presented many cases of how some conservative broadcasters or writers clearly did (or do) present a biased message.
But few people, even political independents, are truly (conceptually) standing on the 50-yard line of the political field, where they can see half the field to their left, and half the field to their right. Many may "believe" they're centered, but in reality, may well be at the 10 or 20-yard line on either end of the playing field, and therefore see only a minority supporting their views, and a large majority seemingly against their views. One thing both the Goldberg books and the Brock book makes clear: if you're looking for bias in a book or broadcast, you'll probably find it.
The down side of Brock's book, to me, was that in trying to drive his point home, he over did it. Give ten good examples, and you start to understand his point. Give ten more and then ten more and then ten more, and you really understand his message. But adding hundreds more examples only becomes mind-numbing. So, to be honest, I fast forwarded through the second half of the book, and don't believe I missed much.
The unfortunate lesson to me, and perhaps to others, will be that you need to take everything you hear on cable news, and see on the internet, with a grain of salt. Much of what is presented may be only part of the story, or a carefully selected group of favorable "facts". If you really want to gain a good understanding of the subject being discussed, critical thinking is a must. Do your homework and review several sources, perhaps even from other perspectives, before you become certain of your position.