It's an intriguing possibility, but my imagination is unequal to the task. If they didn't mind showing us all this evil crap, what horrific secrets are they actually hiding? Secret pacts with Cthulhu? Hitler was actually a USA agent? Nothing big enough seems plausible.

Well, it could be cold war thinking, a line from Dr Strangelove gives one plausible reason.

"Of course, the whole point of a Doomsday Machine is lost, if you keep it a secret! Why didn't you tell the world, Eh?"

Benway's panopticon only functions if the inmates think they are watched. The secret might be that they cannot actually process all the data and are overwhelmed by the sheer quantity of it, in which case the surveillance is more useful if people think they can.