I don't see that as being a solid point because it is pretty challenging to point to an instance of a rare event not happening due to your actions.

The more pressing issue is that the NSA is a group of people. Nobody knows exactly what they are doing, or why, and the only information that comes out is "trust us, we're the good guys". They have a huge budget. Odds are they are massively corrupt and doing stupid things that either do nothing or make America less safe (like mass wire-tapping).