[Jd]

Sometimes it has an easy explanation given typical information asymmetries and incentive structures. For example, you don't give away any of your external intel during a war (i.e. cold war) in the case that you are identifying something by your enemy that might be trying to hide from you. Letting them know you can detect them would be stupid. Also, for similar reasons, record and catalogue every strange phenomenon in case it could be something.

The natural correlate from a citizen perspective is that the government is hiding something (i.e. UFOs). Of course it is, that's the point. But then the point becomes less of a point the less justification there is for wartime behavior, which then leads to increased speculation that the government is hiding something which at some points boils over into widespread public sentiment.

Then at that point there is both incentive to do selective release and for the media to cover it since they know readers want to read about UFOs, etc.

I think that's the Ockham's razor here.

[baybal2]

I don't think one can cover just anything in an open society. Even the truly secret military gear like the original H-bomb, F-117, A-12, anti-powerline bombs, and navy stealth helicopter were impossible to hide completely. At least the fact of their existence was out long before the public saw them.

Even in paranoid USSR, people knew of computer guided recon drones, spy sats, Shkvals, Dvinas, R73 and Strelas — all of which were more secret than the bomb, and were equally bordering on "sci-fi" and unbelievable to the layman at the time.

The leak of Shkval's existence was of particular embarrassment to the Union's military and counterintelligence. Supposedly, there were less than 50 people in the whole Union who were privy to info on them in full, but even before it entered service it became an "urban myth" among civilians in military cities and such.

[narag]

I don't think one can cover just anything in an open society.

If you really want to apply common sense to the hypothesis that aliens are real and here, consider the possibility that aliens themselves have become much more careful since the fifties, just because they know we have more tech to detect and intercept them and governments are no longer able to hide anything.

Or maybe they have a spy net on the ground already.