There are multiple explanations for the Great Silence, also known as the Fermi Paradox. I'd like to explore the idea of the Berserker, a device constructed to destroy and prevent advanced species from expanding into interstellar space.
I have coined the term "Efficient Berserker" to describe the constructs of one civilization whose Berserkers are so powerful and numerous that this single species is capable of policing the entire Milky Way Galaxy. This ties in with the idea of Von Neumann and/or Bracewell probes. The reason we haven't seen any of them yet is that they are quietly waiting for evidence that we have reached a key scientific milestone. Then they will strike.
In the Efficient Berserker Hypothesis there is no need for multiple species to build the probes. And there is no need for that species to survive the billions of years that their probes scour the Milky Way looking for targets. Each probe can build a few more, enough to replace the aging and failing systems, but not enough to create a runaway growth scenario which so frightened Carl Sagan.
The Berserker Hypothesis explains one of the key problems with the Great Silence. Why is it that not one single species has built Bracewell Probes to fill the Milky Way? The answer is that they did, perhaps as many as 1000 different species. Then the Efficient Berserkers hunted them down, destroyed the probes, and then sterilized the system to prevent construction of any more probes.
Every critical question of the Fermi Paradox can be resolved by assuming an Efficient Berserker in the Milky Way. Whether it is radio or optical communication arrays, panspermia craft seeding the galaxy with life, Kardashev II civilizations, Matrioshka Brains, this theory can explain why we humans see no evidence of intelligent life.
If this theory is correct then the human race is on the verge of extinction. One key event such as a neutrino communications array, dark matter energy beams, or maybe just colonization of an asteroid, any of these could lead to our extermination.
This theory can smoothly merge into the Quarantine Scenario, or the Prime Directive. In either of these the Berserker is non-violent, but powerful. It actively prevents species from moving out into the galaxy until we have reached a required level of maturity. It may even intervene in an emergency to prevent us from exterminating ourselves.