Had the first Aliens we met been aggressive, that might have gone well for us, since nothing brings Humanity together like a war against outsiders.
Had the first Aliens we met been totally unlike any other species on Earth, that might have been all right, as a total break from what we knew would allow for a fresh, clean start.
Had the first Aliens we met been like the Greys from pop culture, all large eyes and big heads, that would have made some sense.
But a race of sexy green skinned women? That just led to too many questions…