Very interesting. I wonder how general the roles are. What you talk about at the end is basically bystander effect: I believe that different people are more or less vulnerable to that, and I wonder whether being more 'bystander' prone goes with being more likely to go along with pressure to conform (Millgram etc.) and possibly (to make it clear this isn't a straightforwardly ethical thing) more likely to collaborate in Prisoner's Dilemma. The most important role question might be simply whether you see yourself as a generalised Agent with responsibility for what actually happens beyond fulfilling set roles you've been given.

To quote HPMOR again: 'PC or NPC, that is the question'