What is the Monolith?

The monolith is simply the means of spreading HAL's message.

In today's terms, in America, it is the "Presidential Auto-Cue", or as mentioned above for Feminist Takeover it was Greer's book, and 3,500 years ago for Hatshepsut, it was her Obelisks and for Hitler it was the Reichstag from which he screamed his hate.

For any Monolith the message itself does not have to be well understood, but rather it is the reverence TO the Monolith by those [J Doe right now] WANTING to be ruled to make them feel "safe", even though the bearer of the message might be an ignoramous, as with GWB.

And with 9/11 we had a "Monolithic Sacrificial Lamb" where 2 Monolith shaped buildings were sacrificed as being the False Gods of Globalization or Financial Rule which were taking the spotlight away from the VACANT Presidential Auto-Cue.  As Fahrenheit 9/11 shows, GWB only ever "Thus Spake" to change feet and had to be sent by HAL on a permanent vacation, or Carefully Teaching stories about goats to school kiddies "before they are 6 or 7 or 8" [South Pacific 1958].  So once the 9/11 dust cleared it was back to business as normal, but with a shiny new Monolith to "Thus SPRECH" of Unknown Unknown Terrorrrrrr [the Horror, the Horror - Apocalypse Now 1979].

As Justice Janning testified at Nuremberg about Adolph:

"We had a democracy, yes, but it was torn by elements within. Above all, there was fear, fear of today, fear of tomorrow, fear of our neighbors, and fear of ourselves. Only when you understand that can you understand what Hitler meant to us, because he said to us: 'Lift your heads! Be proud to be German! There are devils among us, communists, liberals, Jews, gypsies. Once these devils will be destroyed, your misery will be destroyed.' It was the old, old story of the sacrificial lamb.
 
What about those of us who knew better, we who knew the words were lies and worse than lies? Why did we sit silent? Why did we take part? Because we loved our country. What difference does it make if a few political extremists lose their rights? What difference does it make if a few racial minorities lose their rights? It is only a passing phase. It is only a stage we are going through. It will be discarded sooner or later. Hitler himself will be discarded - sooner or later. 'The country is in danger.' We will 'march out of the shadows!' We will 'go forward.' Forward is the great password.
 
And history tells how well we succeeded, Your Honor. We succeeded beyond our wildest dreams. The very elements of hate and power about Hitler that mesmerized Germany, mesmerized the world! We found ourselves with sudden powerful allies. Things that had been denied to us as a democracy were open to us now. The world said, 'Go ahead. Take it. Take it! Take Sudetenland! Take the Rhineland! Re-militarize it! Take all of Austria! Take it!'
 
And then one day, we looked around and found that we were in an even more terrible danger. The ritual begun in this courtroom swept over the land like a raging, roaring disease. What was going to be a 'passing phase' had become the way of life."

So at the start of this movie the apes simply touch the Monolith and seemingly get morphed into similar apes but with clothes.  Then the movie itself serves as a Monolith to the many adoring fans who fantasize about the "visual effects and meanings" without ever being able to explain them in American, let alone in English.