the ship was aproaching earth, a planet of harsh climate and being made of mostly water, water being deadly to all known beings, they were not planning on attack

Alien 1: why arent we fighting them? They are so small and squishy!

Alien 2: you dont understand, humans may be tiny but they are built for war, for generations they have fought themselves. If we give them a common enemy at their currently peacful state would mean death to us all!