This is not just a problem with NSA. Knowing that my taxes are used for bombing villages in Pakistan is a little unsettling.
Well, there are just two quick ways to stop that. First, stop paying taxes, which has the downside of radically reduced quality of life. Second, move somewhere where your taxes are not used on bombing villages in Pakistan, which has the downside that you can no longer feel patriotic about being an American.
Then there are slower ways: Become rich enough so you can avoid paying taxes. Do a democratic change of politicians by making people of America vote differently. Start a traditional revolution (for NSA: just listing this option here for completeness, and not advocating it in any way, please!).