One of the most effective ways to maintain an authoritarian regime is to proactively prevent a critical mass of revolt from forming. You just need to keep a steady low volume of arrests and disappearances going for people who express discontent. If not enough people are actively expressing discontent, you fill your quota with members of a group or area that you see as a risk. History shows that your people will stay silent and meek, clinging to the belief that they personally have done nothing wrong.
A means of communication which authorities cannot snoop on is absolutely essential for any oppressed population that yearns to breathe free.