China has lifted 850 million people out of poverty. Percentage-wise, we have far more prisoners in the US. The answer lies in the instability that China experienced in the past leading to the largest famine in human history. They will certainly do what they need to do to prevent instability. Sometimes it is heavy-handed, but as I said in another thread we have Indian reservations, border detentions, hate groups, largest per capita prison population, a high murder rate. We are far from perfect it's easy to point the finger about something that you know less about.
Much like the Chinese would prefer to live under authoritarian but stable rule rather than whatever balkanized aberration a premature and flawed democracy that a billion illiterate peasants living in abject poverty would have produced.