My biggest fear about alien contact isn't that they'll be genocidal towards us.
It's that they'll want to help us out, but get completely fucked up ideas of our nature and needs and situation. And try to implement solutions based on that which fuck us up even further.
If you've read Octavia Butler's novels you know the kind of thing I'm talking about. Also imagining
- Asexually reproducing aliens who can't wrap their brains around human gender/sexual politics
- Biologically eusocial aliens who don't understand how human leaders or ambassadors can not represent their people
- Aliens who don't experience death the same way we do (e.g. share memories the way bacteria share plasmids), and so don't understand its enormous primacy in human lives and culture
Basically I'm thinking less a "Aztec first contact with the Spanish" scenario, and more "NT adult adopting a severely autistic child and having no idea how to raise them."