It is obviously common for journalists to report "both sides of a story" in the "he said/she said" fashion regardless of the nature of issues, and without any objective analysis. This gives the appearance of fairness and balance (as in the slogan of the notoriously partisan Foxnews), while it often helps objectively false views or arguments to have equal footing with reality. As if there is a need to balance truth and lies. For example, Kerry (and earlier Clintons, Gore) suffered a lot from clearly false and even outright ridiculous accusations, because the media gave the rumours "fair" time to present themselves. The same happens with important policy issues, such as Social Security.
Recently, scientific research was done by brothers Jules Boykoff (Whitman College, Politics Dept.) and Maxwell Boykoff (UCSC, Environmental Studies Dept.) on the media coverage of the Global Warming debate.
In the climate debate, the agressive skeptics side (not numerous but well funded by energy industries) is often amply quoted against the scientific consensus.
Boykoffs analyzed articles on global warming that appeared in the 4 largest prestige newspapers (New York Times, Washington Post, Los Angeles Times, and Wall Street Journal). From a total of 3543 articles between 1988 and 2002, they examined a random sample of 636 articles. The results are not surprising.
53 percent of the articles gave roughly equal attention to the views that humans contribute to global warming and that climate change is exclusively the result of natural fluctuations.
35 percent emphasized the role of humans while presenting both sides of the debate, which more accurately reflects scientific thinking about global warming.
6 percent emphasized doubts about the claim that human-caused global warming exists, while another 6 percent only included the predominant scientific view that humans are contributing to Earth's temperature increases.
Through statistical analyses, we found that coverage significantly diverged from the IPCC consensus on human contributions to global warming from 1990 through 2002. In other words, through adherence to the norm of balance, the U.S. press systematically proliferated an informational bias.
The also give a history of journalist principles in the USA.
In 1996, the Society of Professional Journalists removed the term "objectivity" from its ethics code (Columbia Journalism Review , 7-8/03). This reflects the fact that many contemporary journalists find the concept to be an unrealistic description of what journalists aspire to, preferring instead words like "fairness," "balance," "accuracy," "comprehensiveness" and "truth." In terms of viewpoints presented, journalists are taught to abide by the norm of balance: identifying the most dominant, widespread positions and then telling "both" sides of the story.
Objective coverage of scientific issues did not benefit a lot from this change. Neither political debates, clearly.
For other report of their work, check this. It is also notable that Maxwell Boykoff has been active with Peace Corps in helping Honduras overcome devastation by Hurricane Mitch.