When I see something entitled "A Progressive Debate" (particularly on church and state) and described as a "Liberal-Liberal" debate - my hopes aren't too high. Particularly at the Yale Law School, even moreso given that it's sponsored by the American Constitution Society, who does not (IMO) have nearly the same penchant for providing balanced and challenging forums as the Federalists. BUT, all of that said, the idea of a debate (a term I really have begun to loathe as a description of a panel discussion with opposing sides) that could force Jim Wallis to defend the role of religion in the public sphere against Barry Lynn of Americans United For Separation of Church and State might be interesting.
Or, it could just turn into a celebration of how much better they are than the 'religious right,' which would be depressing if that's what Wallis gets reduced to.