I'm not sure what the alternative is. Without some form of surveillance, you're never going to catch terrorists or other bad actors. You do, however, need to make sure there are strong checks and balances in place to ensure that people don't use it for nefarious purposes or for personal gain.
The structure of your statement has problems not related to the topic at all. When you take something away that never (or rarely) happens, how do you establish causality? Suppose I told you that taking bazookas away from people that live in the city prevents bear attacks? You might say that there aren't bear attacks in the city anyway, which would be true, but you couldn't prove it one way or another. Who knows, mayb…
When Sept 11 happened the popular meme for why we were attacked was "Because they hate our freedom." On a strategic level, they're doing a dramatically good job at winning: look at how much our freedom has been curtailed since then. And they can do it without touching an American; rather, the fear of what they might do provokes the U.S. government into destroying our freedom for them.
(A secondary goal for Osama bin Laden was to bankrupt America, something they are also winning at: since 2001 the U.S. national debt has grown from $6T to $23T.)