Perhaps the scariest thing is their plan to collect and store all data on all of your activities, then retroactively mine it. That is, from the moment you use the internet for the first time as a 9 year old until the day you die as an 89 year old, every text message you send, every email you write, every website you visit, and (if you're thinking of becoming a politician) every nude picture you send can potentially be used against you.

The reason this is scary isn't just because of the present social climate. The current social climate is actually pretty decent. The reason it's scary is because social climates can change quickly. A couple decades from now, what you did legally today may be illegal. If you're pursued and prosecuted, it's possible someone may dig through this vast trove of collected data and use it against you.

Clapper (the head of the NSA) has taken the stance that it's okay to collect everything, and that a "search" hasn't taken place until some human actually tries to look through that data. He frequently uses the analogy of a library: it's okay for the NSA to have all the books (everyone's data, everywhere) because a search hasn't taken place until they take one of the books off the shelf and look through it.

The temptation to use that library for purposes other than curbing terrorism must be pretty strong.

I'm going to speculate for the sake of example. It was often cited that one of the reasons for the 9/11 attacks was that the agencies weren't cooperating. As such, there has been a lot of pressure for the agencies to work together since then. I'm going to guess that if the FBI hadn't eventually tracked down DPR on their own, they may have tried to turn to the NSA for help. While it's not clear that the NSA has those kinds of capabilities, they're certainly more capable than the FBI at breaching the Tor network. There are slides out there which say something along the lines of "... we're able to deanonymize individual targets, not everybody at once."

That example is a little bit unrelated to "collecting all data about everybody and then mining it," but remember that if the agencies begin cooperating in that fashion, sharing that trove of data may be the next logical step.

I apologize for speculating, and my speculation should be treated as such. But please realize that just because they're not doing that to Americans yet doesn't mean they're not doing it to citizens of other countries with impunity today.

Here's another ancillary point. It should be no surprise that the NSA could probably find out the identity of Satoshi Nakamoto pretty easily. But my point in bringing that up is this: if Satoshi himself cannot stay anonymous, then what hope do any of us have? Anonymity may be dead at this point. It's pretty clear that humans will continue to live even if that's the case, but a world without privacy is going to be a very strange one.

By the way, I should also mention that the GCHQ may be even more capable than the NSA. There are signs that the NSA are better at pulling off attacks (Stuxnet, Tailored Access Operations) but that GCHQ are better at collecting data (bypassed Google's encryption). It has also been hinted that whenever the NSA runs into roadblocks against investigating Americans, they enlist the help of the GCHQ since it's legal for them to do so (and vice-versa). So even if the NSA is reformed, there is still this spectre of this worldwide data collection and governmental collaboration hovering over society.