Oversight is definitely the key to limiting the possibility of government overreach, but it is wrong on the populace's part to think that just because they aren't privy to the oversight that it isn't there.
There is much the same problem with those who work in the political realm in D.C. They are constantly derided as do-nothing on a macro scale, but on an individual basis a lot of effort is put into how laws are constructed and amended. This is analogue to the situation in the intelligence community -- a lot of work is done by individuals and the organization they are a part of to preserve civil liberties, but disclosing the nature of their collection abilities in the interest of the transparency of their protection of civil liberties is absolutely counter-productive. A big difference between the two, is that the political worker can disclose their work while the intelligence worker can not.
I'm not denying that there are instances of overreach, but I'm merely making the point that the framework for protection of civil liberties is not a piece of glass that shatters on the first stone thrown against it. It is an organic process, which is subject to upper and lower bounds in order to come to rest at a medium level with which both the public is suitably comfortable, and which gets the job done.