People complain that American mainstream media are becoming more and more polarized. There is a tradition in American journalism that the journalist should be objective and report the facts without judgment. Opinion pieces and Editorials are relegated to the back pages.
Nowadays those standards are eroding. Fox News, MSNBC, and CNN have discernible biases but still pander to the idea that they provide objective journalism. Meanwhile there is the perception that this trend is degrading the quality of information.
From a narrow perspective that may be true. I learn less from Fox News if they selectively report information that confirms the preconceptions of their audience. But media bias makes the media as a group more informative, not less.
Suppose I have a vast array of media sources which are scattered across the left-right spectrum. When a policy is being debated I look at all of them and find the pivotal outlet: all those to the left of it are advocating the policy and all those to the right are opposed. Different policies will have different cutoff points, and that cutoff point gives me a very simple and informative statistic about the policy. If the range is more narrow or more sparsely distributed this statistic is simply less informative.
Another way of saying this is that there is social value from having advisors with extreme biases. When I am thinking about a policy that I am predisposed to like, I learn very little from an unbiased source but I learn a lot if a source with my bias is opposed to the policy or a source with the opposite bias is in favor of it. It must be especially good or bad for these extremists to go against bias.