Parenti talks about this in Inventing reality. He was talking about a CNN or NBC anchor who said they don't have to do propaganda or have any bias, their employer lets them say stuff freely. Parenti pointed out that the anchor may believe that, and even their employer may believe that too, but they would never have received this job if they were going to say something NBC didn't want.
The pervasiveness of the superstructure is that it self-reproduces ideology, much like the base self-reproduces class relations.
He gave the name of the anchor btw and pulled from public statements like interviews and such, I just don't care to remember their name.