Isn't this something that has been shown in history time and time again? Look e.g. at recent German history: Nazis abused data collection to find and kill Jews and political opponents, and soviet Stasi invaded privacy to find, imprison and torture political opponents. Beyond this concrete evidence, there is also the indirect impact by the "chilling effect". I believe many or most of us experienced this effect already. So I'm entirely certain that the negative impact is easy to see.