Oh yeah, if aliens really existed with their huge motherships or something, they couldn't really act like in Independence Day (the movie). Something half the mass of the moon parked in geostationary orbit near Earth (like the mothership in Independence Day) would cause tidal waves on Earth sufficient to smash us all underwater. Even if the aliens came in peace, they would leave us in pieces. It would be like "we come in... oops... Earth's gone".