It's not so black and white. People can believe they are doing good. You are helping take down terrorists after all. The majority of the population is ok with this stuff, you don't think the people who work there are?
Not according to polls since the Snowden leaks came out.
Also, I've yet to see real evidence of the mass surveillance over the past decade helping stop terrorist plots. They said it was 50 "terror events". They lied even about those. It was more like 1, and even that wasn't a big deal.