Stalinism, as seen under Stalin and mao, used purges in order to mobilize the society in support of the cult of personality. In order to make the party a tool of the leadership, all people had to be complicit in the mass purge, and those who were not became it's victims.

During the Chinese civil war, Stalin sent instructions to the Chinese communist party that essentially told them force peasants to kill landlords in brutal ways, so that no peace would ever be possible again. This type of cultural complicity In violence was an essential element of these authoritarian regimes. All of the party members who publicly denounced the innocent, or harassed kulaks or "capitalist roaders" were a part of the purge, and therefore couldn't remove themselves from it. This creates an environment of complicity and fear, which allows for total social control.

If you read 1984, Orwell totally nailed it with the character of O'brien