Why were socialist/communist governments in Russia and China so unrestrained in their brutality towards their peasants?

It needs to be seen individually.

Explanation:

In The Soviet Union, the Russian Revolution was essentially an industrial revolution. After taking power Stalin collectivized the farms, wiping out the more prosperous kulaks, and pursued these policies with a ruthlessness, such as in the Ukraine where millions died of starvation. Such action was seen as essential in providing sufficient food for the masses and establishing central, communist control. The unrestrained nature of Stalin's policies also reflect the dictatorial nature of the man and the structure he established to allow him to act in that way.

In China, the revolution was essentially a rural one based on the peasants. Mao's armies were peasant armies and he instructed that the peasants be treated with respect during the civil war and immediately after he gained power in 1949. However during the 50's he too pursued economic policies, particularly collectivization of communes which again led to disastrous food shortage leading to possibly up to 40 million victims of starvation.

there is no chart here so no one can answer this.