The fear and terror he created was unimagineable. I mean that kind of thinking in our current society is just absurd. But the main thing is that Mao knew that the students would be easy to manipulate, they had grown up under Mao's guidance. Mao was their guardian, so when Mao intiated the campaign, everyone queued up to joing the Red Guards. If you were rejected, if would've been devastated.
Teenagers have the inclination to belong to a peer group.
They were also indoctrinated to think that obeying Mao was their purpose in life. The Red Guards were prone to use violence, they were fearless, and had an instinct to fight for what they thought was a just cause. Well, I think this was a very, very tragic era in Chinese history. Being Chinese myself, I fell ashamed, in some way, of this particular episode. My parents are bitter about.