If you are arguing for more government eavesdropping, I would point out that terrorism is a failed political strategy on the decline even without help from government programs.
If you are arguing for less government eavesdropping, I would need to see evidence, first, that there is some sort of real danger. I don't share the libertarian presumption that government is by definition malicious and incompetent.
Concrete numbers would be nice if we had them, but the values offered by true believers are not data driven. In the meantime, I will continue not worrying about getting hit by lightning and, simultaneously, not worry about being eaten by a shark even though one is probably riskier. That seems reasonable to me when there are higher risk things to worry about.
If you are arguing for less government eavesdropping, I would need to see evidence, first, that there is some sort of real danger. I don't share the libertarian presumption that government is by definition malicious and incompetent.