Picture another race dumping self replicating nanobots into our ocean, it would be an act of war.
Read a sci-fi short once where some advanced civilizations would automatically attack any other such they encountered because the other was completely inscrutable, unpredictable and as such posed an unacceptable existential threat. No time to study them. You snooze, you lose. Instantaeous annihilation for just revealing your presence. Totally creeped me out.