Excommunication?

The recent controversy over church courts has led to a bit of confusion and conflation of ideas.  There are three separate issues here.

1- Should the Church excommunicate people?

2- If yes, on what grounds should the Church excommunicate people?

3- If there are legitimate criteria for excommunication, does a specific individual meet those criteria?

It seems to me that most of the criticism of the Church in the blogosphere is based on question one.  That is to say, the critics reject the idea of that excommunication is a valid course of action.  Therefore, any Church court is fundamentally illegitimate.