I guess my overall take on this sort of thing is along the lines of our "innocent until proven (beyond a reasonable doubt) guilty principle in criminal law.
The principle ought to be transparent and open until proven (beyond a reasonable doubt) that is needs to be kept secret.
It seems that governments (including and especially the US government) operate under almost exactly the opposite principle: "Hidden and secret until proven that it shouldn't be."
Both of these principles carry an inherent catch-22 though: How do we go about proving that something needs to be kept secret until we know what it is that's being kept secret. To this point the answer seems to "trust us."
As far as the notion that governments (including the US) are not generally using this as a cover and shield to cover criminal, immoral, not reasonably classifiable information and activities or other nefarious and even embarrassing stuff and that this is merely the paranoia and imaginations of a handful of tinfoil hatters reeks of both ad hominem and the secret keeper basically saying "Have I ever lied to you as far as you know?"
In my view if the state is considered a necessity (and I don't agree it is), it should be kept as small as absolutely possible, as open as absolutely possible,and its restriction and infringement upon peoples rights as absolutely minimal as possible.
Granted that whole "as absolutely possible" thing is open for (sometimes very wide) subjective interpretation. For example some today think anything less that the amount of government we have now is or would be tantamount to anarchy and that right now we already have the "absolutely minimal as possible."
Ideally we'd have some more objective means to judge this.
Personally, I think the defaults ought to be maximum liberty and maximum transparency (of the government's actions and information) with infringements to liberty and secrecy having to "fight" their way into society. Sadly I feel we've crossed the liner to being in the more opposite expression of that. Liberty need to be justified to exist in many cases. Transparency needs to be proven to be necessary in many cases.