A movement that promises a classless society cannot deliver it, because whoever seizes power turns into a new ruling class. The leader who preaches equality ends up living in the old emperor's palace, served like a monarch.
A prisoner with no power can still fight back with sharp reasoning. She can absorb the force of the interrogator's own arguments and turn them against him, as in a martial art. This works even when the two sides are equal in nothing.
When newspapers and leaders praise vandalism instead of punishing it, ordinary young people quickly take over the streets and destroy. The layer of civilisation is thin, and destructive urges sit in everyone, waiting for permission.
A regime that runs on forced confessions needs the accused to agree to their own guilt. Refusing to confess, even through years of solitary confinement, hunger and illness, denies the system the one thing it cannot simply take. This also spares the prisoner the later shame of having betrayed family or friends to survive.
When those in power denounce one leader after another, people eventually see that the emperor has no clothes. Once the regime has lost belief this way, it has to win back support by offering material gains instead of ideology.