Corrected entry: When the Arquillian battle cruiser appears above Earth, all of the other aliens on Earth leave. Later, K tells J that "there's always an alien battle cruiser or a Corellian death ray or an intergalactic plague that's about to wipe out life on this miserable little planet." If that's the case, shouldn't the aliens always be leaving, or just never come back at all?
Moose
5th Jan 2020
Men in Black (1997)
Correction: They are refugees mostly, they got nowhere else to go, nobody would accept them. Plus there is a good chance any other place in the galaxy experiences the same things, but worse.
Correction: This was K's way of telling J that there's always something going on. In this case, the Arquillian's gave a clear warning that the planet was going to be destroyed. The aliens on Earth reacted to that with fear. They aren't going to know about every little job the Men in Black deal with.