The problem with blogs is very simple: there is no quality control. Think about it. Articles that appear in traditional news sources have been vetted by an editorial staff, and have been thoroughly fact-checked before publication. Journalists are also bound by ethical standards. Failure to fact-check, failure to behave in an ethical manner can end careers. News sources that earn a reputation for shoddy reporting lose sponsors and readers. Those sorts of constraints don't exist in the blogosphere (as the bloggers call it). Anyone can start a blog via any of a number of free hosts (Blogger, Wordpress, Livejournal, etc.). One need not have any credentials to start a blog, nor does one need to adhere to any ethical standards or deal with the "inconvenience" of editorial oversight. In other words, it's a perfect breeding ground for kooks and crackpots.
That's not to say that there are no good bloggers out there. I can find a number of legitimate experts, who actually do a good job of providing informed opinions on their areas of expertise, who do present evidence in a balanced manner, and who work hard to earn their readers' respect. However, such individuals are few and far-between. Instead, the blogosphere is littered with individuals who propagate weird conspiracy theories, half-truths and damn lies, hit pieces, and bigotry. The nature of the Internet is one that encourages phenomena known to social psychologists as selective exposure and selective avoidance. Readers of blogs tend to seek out blogs that agree with their own preconceived beliefs, prejudices, and ideological preferences and to avoid those blogs that diverge from them. One consequence is that bloggers are reinforced for saying outrageous things - even if those outrageous things have not been thoroughly researched - to the extent that members of their readership base agree with them.
Bloggers also - at least in the US - can engage in actions such as slander or libel with minimal concern for the consequences. As litigious as US residents tend to be, they tend to have a harder time mounting successful lawsuits against bloggers who spread malicious gossip than might be the case in other nations. In addition, the vast majority of bloggers hide behind assumed names, making it difficult to successfully find and challenge those offenders. Anyone who has been victimized by such individuals will understand the frustration all too well.
My general advice about blogs is to mostly avoid them like the plague, unless the bloggers are ones who are recognized experts, affiliated with some mainstream organization, and who use best journalistic and ethical practices.