On the point of arresting people planning to protest, many protest around the world were fueled by the use of social media/messaging apps. So in that case its not obvious that it has a negative effect on democracy.
I understand your point is that our loss of privacy didn’t lead to arrests or in these instances, but there has almost certainly been arrests in other instances, and we’d be losing sight of the bigger picture if we deluded ourselves into believing oppressive governments, companies, billionaires, etc.. weren’t already heavily using mined data to counter dissidence movements in more ways than just arrests.