Defend the Scrum Master role

Polling all Scrum apologists: Can you help me defend the value of the Scrum Master / Iteration Manager role?

Maybe it’s their [bad] experiences, or maybe it’s their culture, but I’ve been confronted on several occasions by developers who are convinced the Scrum Master doesn’t add value to the team. After all, they say, the SM doesn’t actually do anything. Really?? Where does this particular mindset come from? I just hope this doesn’t go viral, but I have been seeing this attitude in more and more places. Help!? Looking for a collaborative defense here, before I spout all my thoughts on the value the SM adds to solution development and delivery.