That's what you believe. There's no proof that the violation of liberties has actually prevented ANYTHING. As a matter of fact, the entire system is so secretive, complete lacking any kind of check and balances, that you will probably never know. What's worse, we actually know for a fact that things like the National Security Letters, implemented under the Patriot act, were and still are being abused. I mean, tapping calls didn't prevent the Madrid or London bombings, did it? Do you have ANY proof your security increased by tapping of communications?