Exchange trading enhances transparency, by making it clear what's out there and roughly who owns it. It also moves the clearing risk to the exchange; while exchanges do fail, they do so much less often than financial firms, and if intervention is needed, they provide a centralized locus for any private or public action.
Apparently the Chicago Mercantile Exchange is looking at setting up a major derivatives exchange. For those who are convinced that "more regulation", rather than "different regulation" is the answer, strongly encouraging trading on these exchanges would be a good place for the government to start.
This article available online at:
http://www.theatlantic.com/business/archive/2008/10/in-exchange/4226/