Discrimination and Exclusivity

The Supreme Court is hearing a case today about the right to exclude. The University of California's Hastings Law School has an "all comers" policy in which groups can receive school recognition and a small budget by applying and meeting certain criteria, among them is that the group be open to everyone. The campus chapter of the Christian Legal Society joined the national organization and thereby wrote into their charter that gay men, lesbians, and anyone advocating premarital sex could not join. They were then removed from the list of groups receiving school recognition and funding.

Among their arguments is that this is challenging their right of assembly. Of course, it isn't, it is challenging their right to assemble with public funding, but it raises an interesting question. Is there a difference between discrimination and exclusivity?

Fraternities and sororities would violate an "all comers" clause on gender grounds and because they disallow belonging to more than one Greek organization. But what about sports teams, honor societies, or plays? Does the fact that everyone can try out mean that it is not discriminatory even though it is exclusive?