Because talented people don't care about politics, they care about achievements. They don't necessarily care about how their achievements are used. They just want something they can put their hands on and feel content when they make it work.
The most brilliant minds are often bored by the fact they can't find anything that challenge their skills. You give any problem to talent, talent won't care about the nature of it. Talent will be put to work.
And to be honest, maybe the work they do can be legitimate or might serve good in the end. It's just that you will never know about it, for the simple fact that it's classified.
For example, catching tax evasion or financial crimes is very hard. If you really want to catch those criminals (who have the worst effect on society), you might want to step up the spying game and scan everybody. Catching or discouraging terrorists is difficult too.
The issue is not that you scan everybody, the issue is that those spying tools can be used against inncocents or for the sake or private interests. So of course people will scream bloody murder, but if the NSA has a very well made policy to avoid misuse, and if you don't hear about any big scandal, maybe there's no big harm done.
All in all, civilization works in a hierarchy, and politics will lead people to do things. Moral standards are guidelines, they're not rules. Civilization works towards its perpetuation. I doubt those spying tools are used for private interests. I know freedom is important, but you can't escape the fact that information technologies can give new powers to criminals.
The question is, do you want civilization to be the norm, or would you prefer to have people taking advantage of civilization with the use of technology ? I know the US has a history of liberty, but when it comes to domestic telecommunications, I doubt any government will let people use gadget because it feels "free". You're not free when you use any device, any of those device requires telecom infrastructures, and thus it requires civilization.
In the light of dirty finance, I think I can be be okay with those spying program, because I really want those bad guys to be caught. On the other hand, citizens are both protected and housed by government, so I don't think kids can really complain about their parents peeking in their room.
Of course my cynicism doesn't excuse my arguments, but I like to understand the real reasons behind those programs, and children rarely realizes the real reasons the behavior of their parents.
Freedom in modern western countries requires a lot of regulation and very hard police work. Freedom has a very high cost.