Its an interesting theory. IMO: the difficulty of destroying a civilization is probably harder than communicating with them, and the advantages of keeping one around probably outweigh the advantages of killing them if you're already more technically advanced.
A big point in TDF is that the speed of light limits our ability to communicate and understand other civilizations. But, by extension, weapons are also limited by that limit. Of course, maybe its possible to break the speed of light, but then communication could also break this limit.
So, if you're a technologically advanced alien civilization and you become aware of humanity, you can send an Envoy or you can send some Nukes (or, of course, you can do nothing and watch). Just within the context of The Dark Forest Theory, there's practically no reason to send Nukes; at worst, you discover that humanity sucks and then you go ahead and nuke us. But life is probably special; maybe humanity would make great trading partners, maybe our brains function differently and can solve problems differently, maybe our natural proclivity for war would make us great allies, or maybe we'd make great slaves for the mines on the Vartoth 12 colony. All of these are options for a civilization a thousand years ahead of us; they can pick what they'd like, but none of them would classify as a result of The Dark Forest theory.
There's also a possibility that maybe this hypothetical alien civilization tried that course of action in the past with another civilization, and they were friends for a while, helped each other, then fought in a bloody war, and now that civilization is distrustful so they destroy any young civilizations while they still easily can instead of even trying to come to terms. But that's not a Dark Forest theory situation; the Dark Forest Theory suggests that its natural for civilizations to want to kill each other off.
Cixin book covers those aspect pretty well. One of the main element behind his version of the Dark Forest theory is something he calls the "Chain of suspicion". He argues that in a world were communication is limited by the speed of light, there's no way to establish a coherent dialog during first contact between two civilizations that would allow you to completely trust the other party. If you cannot trust that the other party will not destroy you given the chance, then the only way for you to be guaranteed not to be destroyed is to destroy them first. Even if both parties want peace, there's no way for you to convince the other party that you want peace without also giving them the time to destroy you. It's basically a game theory situation where trying to go for peaceful communication is way too risky, and the stake in play are the survival of your civilization. It's also implied that civilization that played the "peace" card will simply get eliminated the moment they encounter someone playing the "destroy" card, making you much less likely to actually encounter a peaceful civilization.
> But life is probably special; maybe humanity would make great trading partners, maybe our brains function differently and can solve problems differently, maybe our natural proclivity for war would make us great allies, or maybe we'd make great slaves for the mines on the Vartoth 12 colony.
Slight digression, and I know your half joking but: I always find the believability lacking in sci-fi that suggest a civilisation capable of faster than light travel could possibly be interested in trading commodities or manual labour of another. Such a feat provides unlimited access to the universe, all materials and energy you could ever need, such a civilisation would likely have basically achieved alchemy transmutation (but for real).
Then, the only thing we posses of possible interest, would be our (and our planet's / ecosystem's) uniqueness, our information, our culture and likely very different perspective of the universe... as you put it "our brains function differently", and they most definitely would, even if only at a cultural level rather than fundamental level. That is something that cannot be obtained anywhere else in the universe, even with FTL, because it's endemic.
> I always find the believability lacking in sci-fi that suggest a civilisation capable of faster than light travel could possibly be interested in trading commodities or manual labour of another.
I think the Stargate universe solved this well; the civilizations capable of building FTL drives (including the one that built stargates themselves) didn't need to trade much with anyone (one of them did use slave labor from other worlds, but for somewhat plot-justifiable reasons). Humanity used increasing amount of FTL tech over the series, but those were either stargates, borrowed, stolen or donated tech, not something humans built themselves - and thus humanity did interplanetary trade.
> the only thing we posses of possible interest, would be our (and our planet's / ecosystem's) uniqueness
That's the core point in David Brin's Uplift saga - ecosystems were the most interesting things a species would own (or rather, lease).
A big point in TDF is that the speed of light limits our ability to communicate and understand other civilizations. But, by extension, weapons are also limited by that limit. Of course, maybe its possible to break the speed of light, but then communication could also break this limit.
So, if you're a technologically advanced alien civilization and you become aware of humanity, you can send an Envoy or you can send some Nukes (or, of course, you can do nothing and watch). Just within the context of The Dark Forest Theory, there's practically no reason to send Nukes; at worst, you discover that humanity sucks and then you go ahead and nuke us. But life is probably special; maybe humanity would make great trading partners, maybe our brains function differently and can solve problems differently, maybe our natural proclivity for war would make us great allies, or maybe we'd make great slaves for the mines on the Vartoth 12 colony. All of these are options for a civilization a thousand years ahead of us; they can pick what they'd like, but none of them would classify as a result of The Dark Forest theory.
There's also a possibility that maybe this hypothetical alien civilization tried that course of action in the past with another civilization, and they were friends for a while, helped each other, then fought in a bloody war, and now that civilization is distrustful so they destroy any young civilizations while they still easily can instead of even trying to come to terms. But that's not a Dark Forest theory situation; the Dark Forest Theory suggests that its natural for civilizations to want to kill each other off.