Bill O'Reilly scares a lot of the media, in part because they don't like their predominately liberal views being challenged by a more conservative, as Bill would call it, "traditionalist" viewpoint. It makes them uncomfortable.
They also resent his show's success, with it regularly being touted as the highest rated cable news program in the United States.
So they try to smear him as some outrageous raving loon, which, as anyone who watches the show and is honest knows, is untrue.
He has opinions that are generally conservative, but not necessarily in lock-step with the Republican party, or the White House. He has criticized Bush for the handling of the Iraq war, and the border issue, for example. He's obviously intelligent, can logically defend his own positions, and hold his own in a debate. I've yet to hear him state these horrible outlandish views of his, he's always accused of having.
Is he out-to-lunch sometimes in what he says? Sure. Has he been wrong? Absolutely. Show me someone who hasn't been wrong once, or said something dumb.
But he's usually right on facts, has opinions that are make sense, (even if they aren't always agreed with) and has an interesting, informative, sometimes entertaining show.