First, criticism, or rather, speech welds actual power in China and can effect real change in the power structure, unlike that in the West where freedom of speech is like freedom of wild animals - free, but powerless. And second, the CCP is actually totalitarian in the reverse sense that it is the total responsibility of the CCP to run every aspect of the country, listen to all the people, and solve all grievances and problems, because if they don't, they lose legitimacy and heads will roll, starting from the highest place then millions. This is coming from both politically Leninist vanguardism and culturally the notion of the Mandate of Heaven.

Now we can argue this form of government lacks checks and balances and likely produces extreme outcomes, but it can also be argued that it is truly held accountable to the people to deliver what the people want in contrast to the west where the government is merely responsible to the strongest lobbies.

That is: The (implied) claim is that criticism could lead to the fall of the government of China (I wish!) or at least to social turmoil, in which a lot of people could die. Given China's history with respect to social turmoil, fearing a bunch of people dying in such circumstances is completely warranted. And thinking about the consequences of your words is never a bad idea.

But when I look at the way China is treating the Uighurs, "people might die in social turmoil" doesn't look like that much of a change from the status quo. In particular, it doesn't look like enough to keep me from saying the criticism of the Chinese government that seems so clearly warranted.