The HPA exists because of a common felt need by its members to respond to the story of Harry Potter and the values and messages articulated by the HP series. And they feel that unfairly traded chocolate is not commensurate with the values of the Harry Potter series, and therefore should not be used to make items that will be connected to the HP franchise.
I get into all of this to say: why don't Christians feel the same way about the Jesus "franchise"? Go into a Christian bookstore and look at all of the Jesus junk that they have: "Christian" mints, spinning tops, chocolates, rubber balls, and the like, all line the shelves of Christian bookstores. First I think we need to ask ourselves: do we need this stuff? It is my suspicion that we don't. But the second thing is if we look into the manufacture of these products, are they manufactured in a manner commensurate with the values of the one whose narrative inspired us to believe? I see in the Harry Potter Alliance a friendly challenge to the Christian community: try to live for Jesus in a way that is in keeping with the way Jesus lived.