Of course, it is true that Dailykos is a liberal blog, brought to you from Berkeley, CA (which I fondly refer to as "The People's Republic of Berkeley"). Thus it is critical of the current Administration. But note that O'Reilly's problem wasn't even with the main posts by Kos writers. No, he was complaining about people's posted responses to posts on that blog. I suppose what O'Reilly wants is for Kos to edit and/or censor the people posting on his blog, because some of them are just too darn snarky for him.
Stephen Colbert had something to say about this last night:
Bill O'Reilly: [Daily Kos is] like the Ku Klux Klan. It's like the Nazi party.
Stephen Colbert: Exactly! The Ku Klux Klan and the Nazis were both notorious for allowing people to express unpopular views in an open and free forum.