- Attacking a planet that may or may not be a threat eventually is a much more expensive, noisy and slow endeavor than a shot in the dark in a forest.
(you can also think about all the technical hurdles such a thing would take, also remember that the fast something goes the harder it is to maneuver and to stop at the destination), don't underestimate all the kinds of noise that such thing will create and can be traced back to its origin.
- No species on Earth do that kind of unprovoked attack, unless it is very cheap and quick (and riskless)
So no, I think there are many better explanations than simply the dark forest one
I think that's where you're wrong. For a sufficiently advanced civilization, destroying another that's around our level would only entail destroying our planet. Hell, destroy the whole solar system to be sure. A "simple" way to do that would be to make the sun go supernova, or destroy it somehow.
How would you do that? There's a tremendous amount of energy already in it, it's releasing it gradually for now but what if there were ways to make it release all at once? One potential approach would be to throw something at it at relativistic speeds (you'd imagine accelerating things to near-lightspeed would be a pretty obvious milestone in the tech tree).
For an advanced civilization, this is pretty easy; they'd probably be able to do it routinely from a mobile spaceship so they don't have to give away their home star's position.
(you can also think about all the technical hurdles such a thing would take, also remember that the fast something goes the harder it is to maneuver and to stop at the destination), don't underestimate all the kinds of noise that such thing will create and can be traced back to its origin.
- No species on Earth do that kind of unprovoked attack, unless it is very cheap and quick (and riskless)
So no, I think there are many better explanations than simply the dark forest one