True, game theory makes it less likely a good strategic first move, but you can always come up with scenarios where a super predatory race has set up the signal

True, game theory makes it less likely a good strategic first move, but you can always come up with scenarios where a super predatory race has set up the signal a long time ago to target nascent space-faring civilizations to preempt them. If the newer civ gets past that, then the aggressive aliens up the threat level and take more drastic action.