I have been working as a software consultant for more than 11 years. Because of that I am an eager supporter of lean principles and agile methods.
Being a scrum master is basically the same as being a coach, in this case team coaching. Coaching is about creating self awareness and making the coachee take responsibility himself. As a coach you are not supposed to reach any goals or solve any problems for the coachee. The same goes for the scrum master, it is not about managing and it’s not about solving the problems for the team. It is about creating self-awareness that makes the team take responsibility and helping the team focus on their task.
Coaching is what makes a self-organizing team.
These articles also come to similar conclusions:
Agile Management is Servant-Leadership (Agile Advice blog post)
Agile Coaching