I fear that in the wake of Keith Olbermann's sudden exit from MSNBC there will be a deluge of comparisons between his rhetoric and that of personalities on Fox News. I have not called them personalities by chance: none of them are journalists. Nor, necessarily, is Olbermann. But the difference is macroscopic, it does not require in-depth analysis. Even at first glance, Olbermann was a giant of journalistic ethics compared to his charlatan "counterparts" at Fox or most of the insipid reporters and pundits at CNN.
I could go on to write a whole new post about false equivalences, the abysmal treatment of reality and facts by Fox News compared with the strong factual basis for Olbermann's rants (his "Special Comments" or his "Worst Persons" segments), or the void that Olbermann departure will leave, a void that can only be filled in part by the superlative Rachel Maddow.
Instead, I will link to A Tribute to Olbermann: Why He Is Different From the Pundits at Fox News. It sums up everything I would have come up with, and does so with more clarity than I could have mustered.