I think that it can be very easy for one voice to call a crowd to action, but it depends on who the person is.  If the person is well respected and has respected ideas then it is easy for people to turn to the person that seems to know what they are talking about.  Richard came into the communist group with little idea about what kind of group the John Reed Club even was.  But, after he expressed a couple of his ideas people turned to him and he was soon nominated as the leader of the group.  When Comrade Young come to the group people started to respect his opinions when the saw that he was an amazing artist.  When he started accusing Swann as working with the police people did not go against him because they truly believed that he was a credibly source.  If a person looks credible and has a reputation at something people are quick to turn to someone that seems to know what they are talking about, because many people need guidance and someone to follow to affirm what they think is true.