But it doesn't, unless it is extensive/complete. It just seems like it does because censored media is constantly reassuring us that the censorship is working, and that all reasonable people enjoy it.

You can't destroy ideas by censoring them from the largest outlets, you have to perpetually search out the smallest outlets (e.g. open everyone's mail) to make sure that these ideas aren't still infecting people, multiplying exponentially. You can't relax anywhere, for a moment. The only surefire way to kill or silence ideas is to kill or silence the people who hold them. That means you have to have systems in place to detect stray ideas, and processes in place to eliminate them.