Except they could say exactly that and none of them do, and over time incidents /can/ be revealed to the public where surveillance was instrumental in stopping

Except they could say exactly that and none of them do, and over time incidents /can/ be revealed to the public where surveillance was instrumental in stopping terror/hunting down terrorists/preventing attacks but it never has been. Their crowning achievement was locking up a taxi driver who gave to a Muslim charity overseas that spent some of its money on terror. Don't you think the surveillance boosters would love to provide proof that it actually works while right now all we have is proof of its failures? "Classified" information can be quickly declassified if it helps the public perception of intelligence agencies; Zero Dark Thirty was a propaganda film built on classified intelligence leaked because it made intelligence agencies look good and glorified torture. Incidentally, the people who leaked information for that film were surprisingly not targets in Obama's war on intelligence leakers.