It's orders of magnitude of orders of magnitude less energy to communicate with (including obscuring your origin, if you want) than destroy a civilization. And communication has potential benefits (cooperation) that destruction does not.
Civilizations that communicated would very quickly and easily out-compete/out-advance civilizations that did not. "Malevolent" civilizations would inevitably run into more advanced cooperating civs sooner or later and be checked, either learning to cooperate themselves or lose.
Put another way, the assumptions used to build out the hypothesis, "Chains of Suspicion" and "Technological Explosion", don't make sense either. "Chains of Suspicion" assumes civilizations cannot communicate, yet the dark forest hypothesis assume civilizations can destroy each other. That's a contradiction. If you can physically interact, you can communicate (and as I pointed out before, with much, much less energy/resources than it takes to destroy). And "Technological Explosion", as written in the book, assume exponential technological growth could occur at any point, which seems to be nonsense to me. Any kind of exponential growth necessarily depends on a medium primed with the resources for that growth and stops when the resources are expended (which is never all that long, given the nature of exponential growth).
I cringed every time this idea was forced into the forefront of the books. They are such great and imaginative books, I don't mind at all that not all the ideas really pan out, but it was a little hard to stomach every time the plot turned on this weak idea.