There is also sometimes a quite large change in the mentality of the single officer going about normal daily duties and the one in a group moderating a crowd of civilians in a demonstration or at a social event.

They quite rightly have to worry about mob mentality but don't see the same potential in themselves. Or if they do, it is only retrospectively. Police men and women are after all human beings. They are just as likely to behave instinctively in any "us against them" situation.