Lt. Col. Anthony Shaffer knows a little bit about data mining; he was a primary player in the project known as Able Danger that was shut down about one year prior to the 9/11/01 attacks. Here is Shaffer on Fox News, debunking the claims that PRISM prevented the NYC Subway attacks. Details about the leaked, top secret PRISM program actually reveal a program than makes it more difficult to go after terrorists and thwart attacks.
Think about groping grandma at the airport and transferring that counter-productive strategy to surveillance.
In short, the more information you collect, the more difficult it is to sift through it.
h/t GWP