I think this fantasy persists because it is sometimes true, for a short period of time or for small groups of people. However, such a state is like a body witho

I think this fantasy persists because it is sometimes true, for a short period of time or for small groups of people. However, such a state is like a body without an immune system: it will happily continue along its path until it encounters a disease and then it gets ill. Likewise, a leaderless group can work very well for a while until someone joins the group who will put their own interests before that of the group. Then the group has much less capable defenses than a traditional hierarchy since by definition there is no leader to expel the new person. The chance a group meets such a person is clearly dependent on both the size of the group and the lifetime of the group. In physical terms you might say that such groups are in an unstable equilibrium: any pertubation away from perfect harmony leads to a total collapse because there is no more benefit to cooperating if there are non-cooperators present.