You are right and wrong.
There have been thousands of leaks.
And, the government's ridicule etc. disinformation efforts succeed exceedingly well.
And, 100's of people have been Fosterized.
Shoot--even in 1947--Brazelton was kept naked in a jail cell for days and threatened with extermination of HIS WHOLE FAMILY. That's just a fact. Of course, you don't have to accept it.
But such things tend to silence the more hazardous quite well enough.
There have been tons of things very well kept secret. I know enough to know that. I've read plenty classified traffic.