Comment by HybridCurve

It seems to me that any technologically advanced civilization that is capable of completely annihilating another at such distances would likely be equally capable of avoiding detection, thereby reducing the potential threat level posed by the less advanced civilization. Avoidance would seem to be the best strategy unless the civilization posed a direct and imminent threat. Otherwise, the more advanced beings risk exposing themselves (by deploying a weapon) and declaring to the universe that they are both hostile and aggressive to others.