Obviously known-intelligent life would be a priority, but if they can't get around to the lower priority stuff in 2.5 billion years, well, why should we take the Dark Forest argument any more seriously than any of the other civilizations we've cruised by in the past 2.5 billion years?

The amount of energy available to even a single solar system, let alone all the advanced galactic civilizations that are supposed to be out there, dwarfs what it would take to sterilize Earth. And don't think I'm underestimating that quantity; it's larger than any impact real Earth ever sustained, and it has sustained some doozies. But what's in even a small star, even in a small star's yearly output, is orders of magnitude larger. And this is with the relatively expensive brute force method too; if you're willing to roll the dice on the target not having intelligent life a few steps above where we are now, you could probably put together a gray-goo-esque replicator that would conclusively eliminate any civilizational threat from a given planet permanently, for the cost of delivering a few kilograms of payload to the target system, which is presumably trivial for our advanced civilizations.

As I said, I'm still pretty much on the "yeah, we're probably effectively alone" side, because when you really treat the "the universe is full of advanced intelligent life" idea seriously, you just don't get what we see in our sky. Not least of which is the wide variety of ways in which we simply shouldn't exist, because our ecosystem should have been wiped out one way or another, be it by raw destruction, or simply interaction with some other much more advanced ecosystem that simply steamrolled Earth's primitive life the same way we steamroll an ant hill, a billion years ago. Just about the only way to save the hypothesis is that we are the "Progenitors" and the universe is full of intelligent life if you look at a random place and time, it's just that the "full of intelligent life" hasn't happened yet. If the universe as a whole is full of intelligent life, there still has to be a first set of civilizations, and while every individual in those civilizations may rationally say "the odds of me being here when the universe is empty are as good as zero", there still have to be some "lottery winners".