[westiseast]

Generally they are afraid they (the CCP) will lose control. That's it.

The censorship blocks alternate opinions from forming around issues everyone knows about - for example everyone knows about the Cultral Revolution in China, but the interpretation of it is strictly controlled by the gov in a way that protects the CCPs legitimacy and Maos legacy.

It also stops news about the broken state of the system ever being revealed. For example corruption - occasionally a corrupt official gets 'outed' on social media and when that happens, the government often has to do something - the official gets sacked or investigated. BUT, it's rare it gets to that state. Now imagine if they had a free press or free internet - they'd have to sack half the government within a week, given the scale of the corruption!

Finally, most of the censorship is also aimed at killing activism before it even starts. Online movements never get off the ground, people never coalesce around an issue, the power of the people is never allowed to gather and grow to rival the power of the state/police/political elites. Censorship often aims to keep people (politically) ignorant, isolated and apathetic.