Simplest answer
Why do liberals keep fighting the obvious conclusion? Nobody else is kidding themselves. If you have no trouble admitting that Fox News leans right, why so resistant to the rest?
It's not unusual to hear that lament from paranoids. I think there's a bit of self-aggrandizement, in a perverse way, in imagining that you're the underdog struggling against a hostile world.
BTW, I love that "nobody else" bit. You mean, everyone who isn't a Republican? Who's this "we", Kemosabe?
On the one hand there's Fox News, one network identifiable by name and to be found reliably on one cable channel, which can be watched and its many biases recognized and quantified.
On the other hand, you offer up a vague, vast liberal media conspiracy; or in the slightly less paranoid form, you imagine simply that everyone's hand is raised against you. Very romantic picture. But much of it's based on the third, and worst, of Disraeli's taxonomy of lies: statistics. You compare the number of times that a politician's party affiliation is mentioned--more often for Republicans--and conclude that it means that news people consider Democrats "normal" and Republicans "exceptional" (which is actually not a bad thing, but you miss it because you're looking for insult, not recognition). Or you compute the ratio of good versus bad news from Iraq, and conclude that the preponderance of bad news is evidence of bias, as if the news is somehow obligated to provide an even balance between good and bad. Don't you get that if news agencies made an effort to balance the good and bad news they'd be guilty of introducing a bias into it? The news is what it is, and blaming the messenger for bad news is simply childish.
Then there's the surveys of political affiliation in the news business. Along the way, did anybody check the affiliations of the people who run the big corporations that the news people work for? No? Funny that. But more the point, so what? Is a banker any less qualified to handle your money because he's a Democrat and not a Republican? The existing news organizations (unlike bloggers, for example) have standards they adhere to just as a banker adheres to standards of fiduciary responsibility. It's the definition of professionalism to do one's job regardless of personal opinions.
What do you want? A party affiliation quota in the news business? Affirmative action for the poor downtrodden Republicans? Do you realize that you're wallowing in the same pit of victimization self-pity that you claim the poor and minorities wallow in? Don't you claim to be superior to "those people"?
