No officer wants to be involved in a justified use of force proven unnecessary after the fact, any more than soldiers in Iraq and Afghanistan wanted to make what proved to be the wrong decision in a shoot-don't-shoot situation. Those decisions, even if justified, live with you forever, believe me.
The NSA is not listening to anyone's phone calls. They're not reading any Americans' e-mails. They're collecting simply the data that your phone company already has, and which you don't have a reasonable expectation of privacy, so they can search that data quickly in the event of a terrorist plot.