Two things to notice. First, Matthews' introduction of Murtha perpetuates the myth that a renowned hawk has suddenly turned against the war. A renowned hawk is what Murtha is, but as many, many bloggers pointed out immediately after Murtha made headlines, he's been saying exactly the same thing about Iraq for more than a year now. This is a manufactured story.
Second of all, it is remarkably disingenuous for Murtha to talk about how his recent visit to Iraq changed his mind about the war. If you listen to the full interview, he also lists a number of other recent data points as contributing factors. In other words, Murtha himself is now peddling the myth of his sudden conversion from hawk to dove.
That's quite misleading, and Chris Matthews is embarrassing himself by lapping it up.