It's an interesting idea. I don't think it's necessary, but it may be convenient.
A peculiar feature of the idea is that it may not be desirable for the individual roles to be rational. In order to best fulfill certain roles, the people playing the part must play up the aspects of themselves that do what the role requires and stifle the aspects that serve the functions of others.
If you've taken up a role of generating new ideas, you need to lower your standards so that you're free to come up with things you wouldn't normally think of; if you're the skeptical evaluator for the group, you have to have very high standards and not offer any slack.
"It may not be desirable for the individual roles to be rational."
Exactly! Group rationality may be easier to achieve by encouraging "irrational" verbal positions. Of course, playing a role doesn't mean believing it; so the actual people behind the roles would have more rational, less one-sided beliefs.
In Reply to: Rationalization, Epistemic Handwashing, Selective Processes
Eliezer Yudkowsky wrote about scientists defending pet hypotheses, and prosecutors and defenders as examples of clever rationalization. His primary focus was advice to the well-intentioned individual rationalist, which is excellent as far as it goes. But Anna Salamon and Steve Rayhawk ask how a social system should be structured for group rationality.
The adversarial system is widely used in criminal justice. In the legal world, roles such as Prosecution, Defense, and Judge are all guaranteed to be filled, with roughly the same amount of human effort applied to each side. Suppose individuals chose their own roles. It is possible that one role turns out more popular. Because different effort is applied to different sides, selecting for the positions with the strongest arguments will no longer much select for positions that are true.
One role might be more popular because of an information cascade: individuals read the extant arguments and then choose a role, striving to align themselves with the truth, and create arguments for that position. Alternately, a role may be popular due to status-based affiliation, or striving to be on the "winning" side.
I'm well aware that there are vastly more than two sides to most questions. Imagine a list of rationalist roles something like IDEO's "Ten Faces".
Example rationalist roles, leaving the obvious ones for last:
Due to natural group phenomena (cascades, affiliation), in order to achieve group rationality, there need to be social structures that strive to prevent those natural phenomena. Roles might help.