Hey Chris, I think you are missing Pettit's point. I understand what you are talking about, the psychology and ethics of groups. Diffusion of responsibility is a heavily studied area with examples like the Stanford prison experiment and the murder of Kitty Genovese. What I think Pettit is talking about is much less studied(can't find much on a google search) and much more interesting. He is talking about a kind of logical paradox where a group of completely logical agents can vote for something that is against the will of the majority of the agents. This Paradox would hold even if agents weren't humans but completely rational beings. This is my take on it anyway. I find this episode of philosophy bites particularly good. You could even use this as an argument against direct democracy, which I have always thought was a good idea.