When I am feeling exceptionally pleased with myself, I repeat what I said elsewhere here. This is what I said on Majikthise about journalistic objectivity:
I've been thinking a lot recently about objectivity in three fields: science, jurisprudence, and journalism. I've been tempted for a long time simply to rank them. Science has the best model of objectivity, followed by the law, then journalism.
But really what distinguishes the three is only the amount of time they have. Scientific results are always tentative, because we have the rest of the history of the human race to correct them. This also means that we can develop elaborate systems of peer review and cross checking. The law has some time pressure: people are entitled to a speedy trial. There are fewer appeals. Journalists have to have the story in the next day. There are really no checks whatsoever, so the journalist has to make due with the trappings of objectivity, like never using the first person pronoun.
So what do scientists do with their time that lets them be more objective? At least part of what they do is develop a loyalty not just to ethical values but to epistemic values. They feel duty bound to be skeptics, and question others beliefs; to be epistemically humble, and question their own beliefs; to be curious; and to be diligent. It turns out that the cure for the bias brought by values is simply to have other values.