Orac's got the story. It seems Keith Olbermann let himself get played by the antivaxxers. He let his hatred for Rupert Murdoch override any critical thought he might have had. I liked some gems of his I saw on YouTube, which were generally limited to denouncing obvious evils, but if he's so vulnerable to genetic fallacies, I think I'll be ignoring him from now on.
This antivaxxer manufactroversy is a science matter. You go with scientific consensus and use the scientific method to debate it if you want to know what's really going on. There's no other rational way to look at it. It doesn't particularly matter what other journalists say on the matter, unless they've really looked at the matter scientifically.
So, unless Olbermann really shapes up and admit the full depth of this failure, I think I'd be inclined to favor something like Orac's view. This story makes him into another Bill O'Reilly, only in a different spot on the political spectrum.