A crucial problem is that we're not, or we shouldn't be, particularly afraid of "terrorism" -- a slippery word that tends to be applied arbitrarily and politically.
What we should, and can justifiably, be afraid of is "black swan" security events (such as 9/11). The Boston Bombers were horrible people, but they weren't threats to national security, and the bombing wasn't a "black swan" event. If (and these are big "ifs") the NSA is meaningfully restricted to defending the U.S. against foreign governments, and meaningfully restricted to uncovering plots to kill thousands, then I don't see where the privacy concern is.
What we should, and can justifiably, be afraid of is "black swan" security events (such as 9/11). The Boston Bombers were horrible people, but they weren't threats to national security, and the bombing wasn't a "black swan" event. If (and these are big "ifs") the NSA is meaningfully restricted to defending the U.S. against foreign governments, and meaningfully restricted to uncovering plots to kill thousands, then I don't see where the privacy concern is.