To me the biggest challenge for your argument is the slow speed of light on a galactic or universal scale. The galaxy is tens of thousands of light years acros

To me the biggest challenge for your argument is the slow speed of light on a galactic or universal scale. The galaxy is tens of thousands of light years across and we have only been intentionally emitting radio waves for about a century (and primarily not powerful or well-aimed ones). If you imagine that civilization can commonly be detected by radio signals, but that life in general doesn't do anything particularly noticeable at interstellar distances, only a small fraction of the galaxy would have been in a position to notice us so far (and if they then sent physical objects to attack us in reaction, those objects would be far slower and wouldn't have arrived yet). You might say that there should be probes already dispersed throughout the galaxy, including nearby us, if there are sufficiently powerful civilizations, and that we should have been detected by those probes, and (in the Dark Forest) subsequently destroyed. That might be right, but again, if the probes themselves are only able to detect us but not to attack us, there might still not have been time yet for the reports to have reached their headquarters or for an attack to have returned (I guess depending very much on exactly what conditions they attack in response to).