It is interesting that the dominant mainstream corporate media is able to control the narrative by releasing stories and attention on themes. Most of us have heard of "spin" which is the bias and slant that a storyteller has. However, what is deemed unacceptable subject matter is just how dominant mainstream corporate media deem target topics unacceptable subject matter. They can disempower or diminish awareness of a story (and the lessons we could learn from it) by deeming it unacceptable and unimportant and make it seem worthy of general ignorance. This creates a sort of tapu.
As such, when they wish to keep a secret from a great number of people, they ignore it.
And when it gains enough attention (due to collective or special interest) that it almost demands some kind of attention from anything calling itself "The News" or otherwise supposedly responsible journalism, they can do several things that work to control the narrative and its power.
1. Release some minor attention on it, with a great deal of heavy judgement about why attention is on it and how we should feel about it, in an attempt to sort every aspect and even prevent the reason the original voice gave it attention. This is a last resort and (in my observations of today's society, though perhaps this is changing) only works infrequently since inevitably the points that fail work just as well as the points that succeed to justify the discussion in the first place.
2. Dismiss the subject as a "conspiracy theory" or "crazy" or any other pejorative slur. This weirdly does work as a means of perpetually demoting a topic and claiming it's unimportant while still storing it in the public imagination as something minor. Its role as a "topic that interests outcasts" or "minor topic" occupies any available attention for it in public discussions. It creates a buffer of awkward interaction around any mention of it, which takes up social time and effort to overcome. It may indeed be a minor point in the end, but wrestling with the resistance to considering "outcast ideas" alone overpowers the meaning of the topic itself.
3. Following government and/or military operations finally having reason to use the idea or promote it in favor of other ideas, they can drum it up with not just a hit piece but an entire campaign. The campaign means to promote the idea to "acceptable" discussion and control how its viewed, including catering it to multiple demographics, in order to create a semblance of fairness and sometimes disguise the government and/or corporate media reason for attention on it. The stories or ideas that contradict it will "sink" and therefore the new information supersedes the old, no matter how equal the opposite ideas might be in a fair & open dialogue or debate.
~and~
4. Run a series of concurrently followed stories that have little basis or relevance to actual reality. This was once called "Fluff" but it has advanced in our day to a promotion of actual hoaxes, supported by the other three powers above to prevent them from being questioned and exposed. Having essentially fake or non-issue stories lead as much as possible gives the propagandist several subjects to promote instead of any truth at all. When a source reaches this level of deception and avoidance, it begins to damage and eat away at the credibility of the source, no matter the enormity of it. It could be a government, organization or status that seems undefeated but it's a shell game that is exposed. So in order to maintain some credibility, they will also promote ideas with more basis in reality. Although the game is to lead with fake and useless ideas as much as possible, to prevent the power of public discussion of reality.