One of the most obvious means we have of telling that Fox News is not a news network is its revolving door between Republican politics and and Fox "news." The network is run by Republican operatives and employs Republican politicians, strategists, operatives, and hacks as hosts, commentators, and analysts. The line between what is supposed to be journalism and Republican propaganda is blurred out of existence.
So when Howard Dean steps down as DNC chair and moves on a few months later to guest host two episodes of MSNBC's Countdown I'm not exactly thrilled with another network deciding to create a revolving door between Democratic politics and what is supposed to be objective journalism. Sure, having Dean guest host might generate ratings, but it's not worth sacrificing your credibility.
There ought to be a distinct line between politics and journalism, and having someone so heavily and currently involved in Democratic politics fill a spot that is supposed to be reserved for a journalist blurs that line beyond distinction.