Dissent is not confined to signing public petitions or marching together. Dissent is every time you disagree with something in thought or action. And sometimes that disagreement means taking action that is more personally costly than signing public petitions or expressing your views via social media. Sometimes dissent means that you have to take the government or a business to court for denying you your legal rights. Land disputes when the government acquires land, discrimination at educational institutions, tax and pensions disputes are only a few examples.
With unfettered surveillance, every time you disagree with the state, they can take advantage of the huge imbalance of information between them and you. They can put you under pressure to concede or use information that you did not even know they possessed to embattle you in court. And their story need not be true. The availability of mass data does not automatically reveal the truth. The truth has to be extracted from it. The details of your phone calls, movements, purchases, demographics and social interactions can be used to construct any number of different truths. So how comfortable are you with having the intimate details of your life in the hands of unknown people who can interpret them as they wish?