I think that a small handful of the GB really do believe it all (the oldest and most ignorant ones). But I honestly think that youngest GB members know that its all bunk. Its likely that nearly all of the rest in the highest echelons know this too.
They keep the GB and the whole FDS ideas around only so that they can exert control over the rank and file and to exploit them. Many of those in higher ranks initially learn to work with the dissonance because its an alright lifestyle for them. They eventually are so calloused that they see nothing wrong with using others. I believe that a small but powerful portion of those running the ops were always manipulative parasites and knew opportunities when they saw them.