Through the 20th century there were many attempts to reduce capabilities to express dissent, from outlawing of opposition political parties, to shuttering independent newspapers, to mandatory registration of typewriters. These all made dissent more difficult and riskier, but they did not remove the capability. It was still possible, for one person, or a group of people, to organize in secret and get their message out. They did it illegally, and at their own peril.
My sad observation is that we are quickly reaching the point, perhaps for the first time in history, where governments will have the means to eliminate even the capability for illegal dissent. I believe this is a destabilizing threshold to cross.
Consider the following thought experiment. Imagine we are back in 1985, back in the DDR, but instead of typewriters, you have all the 21st century technological facilities, the internet, Twitter, Youtube, etc. You are a dissident and I am the government.