Bias is effective only if, and only to the extent that, it is undetected. If you tell me that you're a liberal, for example, or that you oppose the war in Iraq, I will pay close attention to what you say. I won't dismiss it out of hand, but I'll be alert for signs of distortion, falsehood, and exaggeration in your factual claims. One way to hide one's bias is to use loaded terms. Read this news report from today's New York Times. Do you see the expression "extricating American forces [from Iraq]"? How does extrication differ, if at all, from withdrawal or redeployment? To extricate is to "free or disentangle from a constraint or difficulty" (The Oxford American Dictionary and Language Guide, 1999). To withdraw is to "remove or take away" (ibid.). The meaning differs, doesn't it? Saying that the president plans to extricate troops from Iraq implies that they are stuck there, or that they are having difficulties there. Saying that the president plans to withdraw or redeploy troops has no such implication. "Withdraw" is neutral. "Redeploy" is neutral. "Extricate" is loaded. Which term should appear in a news report? By the way, other people have pointed out that the mainstream media are stuck on Vietnam. The metaphor of a quagmire—with or without the word "quagmire"—is used repeatedly. A quagmire is a kind of difficulty from which one must be extricated. See the connection? The Times is trying to hoodwink its readers into viewing the war in Iraq as a quagmire. It wants its readers to think the war is a failure and to blame the Bush administration for prosecuting it. It's one thing to say such a thing on the editorial page; it's quite another to say or imply such a thing in a news report.
The Biased Times
My favorite example is the "massive" tax cut. Neutral language would require the journalist to provide facts about the current size of the tax cut (expressed as both an amount and a percentage), relevant historical data about budget sizes and prior tax cuts, and projections from various competing bodies about the predicted economic impact of the tax cuts. All these factors are useful in allowing the reader to decide the proper magnitude of the action. But (a) that takes up too much room, (b) it may lose the reader's interest, and (c) it may lead the reader to believe something that the journalist doesn't.
And so all that work is done and all problems solved by using the term "massive" which, of course, connotes that it's too big. The journalist is happy because he solved problems (a) and (b), never realizing that some of his warm glow comes from his having solved (c).