I disagree. I think the U.S. gov't has had ample time to perfect many methods of establishing and maintaining secrecy through military order and fear in its 230+ years, especially the past 100. If you've ever had any friends or relatives in the military, you may very well know how much fear soldiers live in from losing their freedom and cash flow if they disobey direct orders, not to mention the shame of a dishonorable discharge. I actually have a friend who worked at a very low level of the NSA and he explained how they managed to keep covert operations covert: it's all based on a need-to-know system backed by legal ramifications (i.e. fear). That didn't stop him from reading documents he wasn't supposed to read when he was couriering them, which he called "enlightening and frightening", but it DID stop him from doing anything about it, and he certainly would never talk about what he saw while he was working for them. Another friend of mine from the DOD (Dept of Defense) has also confirmed the level of secrecy and demand of total forfeiture of privacy. She actually stopped talking to me and all her other friends during her first couple of months so that we wouldn't be submitted to gov't snooping on Facebook and what not cuz they gave her a disclaimer that they would be doing that as soon as she was hired.
What I'm saying is that you seem to have this idea that it's all in our heads or something, but many conspiracy theorists base their ideas on a reality that I think you are ignoring in the name of skepticism.
So I dunno... You can sit there and say that things were done in the 50s and 60s they have never been done since, but that sounds very naive to me. Secrecy has a purpose. When whistle-blowers come out and then disappear, what do you think that is about? Disinformation maybe. Or maybe they were paid off or silenced in some other way. Either way you look at it, you can't possibly be serious if you say that you believe that just because there are no declassified documents to prove it, it isn't happening. Cuz if you are, then I feel bad for you.