That’s what Singer’s civilization wants you to think before they send a Photoid or Dual-Vector foil (but later would require a supervisor’s approval which is a PITA)
Pair-instability can only happen in low-metalicity surroundings.
The big bang created hydrogen, helium, and small amounts of lithium. Any higher elements are created by stars, and a significant presence of those "metals" will take a star down a different path than pair-instability.
Low-metalicity environments are not likely to be friendly to life.
I like to think there's a solid argument against dark forest that even if you can destroy other intelligent systems, then hidden intelligent cautious systems may exist and see evidence of what you've done, so there's a potential consequence to destroying every intelligent system you identify.
And then also (maybe this is absurd) isn't there something intrinsic in intelligence to want to avoid conflict and desire peace?
Once a civilization reaches a certain tech level, it can do interstellar travel & by the time you find about it due to light speed delay, it might be far too late to strike - not to mention what size & tech level they might be by the point your first strike wave arrives given the time scales of sub light travel.
So it might be better to use the tried and tested terrestrial nuclear MAD doctrine & rather doe careful diplomacy with any newcomers, like a bunch of psychos each having a full arsenal of planet killing weapons (because that's what any sufficiently advanced civilization is).
In short - rather than Dark Forrest I imagine a harmonious if not utopic galaxy teaming with varied life that is on the first glance peaceful and cooperating.
With the occasional bunch of start systems evaporating once in a while, but we don't talk about those.
A more powerful hidden intelligent system will probably fear a medium power intelligent civlization that sets out to destroy "newcomers" as a civilization that might cause their destruction so the best course of action would be to destroy the medium power one before they become as powerful.
Once multiple destructions have occured, every sentient party capable of becoming aware will fear the others.