Just because the left and right claim that the media is biased against them doesn't mean that one of the claims is not correct.

My Libertarian co-worker's standard answer to my claims of media bias against the right is that the left makes the opposite claim about the media being biased in favor of Bush. Just because two sides make opposite claims, does not mean that the claims cancel each other out. It does not automatically make the media balanced. If one sibling steals the last cookie and when both siblings are confronted by their mother, the guilty child claims no knowledge of what happened to last cookie, and the innocent child also claims no knowledge of the cookie's disappearance, that does not mean that both siblings are telling the truth. One claim is factually correct, one is not.