The collection of metadata about the telephone calling habits of ordinary Americans is ust the sort of thing that an authoritarian government would need to keep its population under control. By using location and numbers called, you can tell who is white, black, Hispanic, who is Muslim catholic, or Jewish, who is rich or poor, who is politically active as a liberal or conservative. The information is all there in the big data that NSA is collecting, but NSA promises they won't mine the data for that information. Maybe it won't today, but what about tomorrow.
Today the system targets Muslims who don't like America. Tomorrow it could be Jews who belong to the ACLU, or Christians who belong to the NRA, depending on ho is in charge. The information is all there in NSA's computers; it just depends on who is processing it, and what they do with the results.