Who are the gatekeepers of dissent?

Who really controls the "alternative media"? When I think of "gatekeeper" Noam Chomsky comes to mind. 12 years or so ago I started buying Noam Chomsky's books, and that was were I learned about the many aspects of American support for undemocratic governments around the world, and the self-censorship that the media goes through in order to maintain the illusion of our foreign policy existing to spread democracy and stability world wide.

However, there are some topics that are conspicuously absent, especially for a man that is as highly intelligent as Dr. Chomsky.

I have seen a couple of youtube clips a couple of years back where Chomsky doubts the involvement of factions within our government having anything to do with 9-11, and doubting whether a "New World Order" even exists. Is he a gatekeeper of dissent?

Now we have Glen Beck and Rush Limbaugh and other "mockingbirds" repeating a threat for a global "new world order" who even 3 months ago refused to acknowledge it's existence, and focusing the blame on "the liberals", while not yet touching on the point that things stay much the same no matter which faction holds office. This leads me to believe that these people could be knowingly withholding information that would lead to the bigger fish that need frying.

So where does self-censorship end and direct propaganda based on orders on high begin? Who else discusses seemingly "subversive" ideas about conspiracies but leaves out information that could really disrupt the status quotient and point to the real bosses?

What is being left out?