Today we have news for conservatives and different news for liberals. That's stupid. News doesn't need built in commentary. Now it seems like history is going the same way. We will have conservative history and liberal history. But I hope not.
History is story telling about a period of time for which we do not have easy access to all the information, nor full access to the participants and their motivations and self-conceptions. In addition, even with the benefit of hindsight, it is common to be unable to identify conclusively which possible elements of the story are the most significant (and as a corollary, which are cotemporal but irrelevant). Consequently, there are different ways to tell the story, and no "objective" set of rules to decide which to choose. Like all human story telling, history must come with a point of view that is critical in framing the elements used in the telling.
Now repeat everything I've just said, but substitute "news" for "history".