Good story, and a nice illustration of many of the points you’ve previously made about cross-species morality. I do find it a bit disturbing that so many people think the SH offer doesn’t sound so bad – not sure if that’s a weakness in the story, commenter contrarianism, or a measure of just how diverse human psychology already is.
The human society looks like a patched-up version of Star Trek’s bland liberal utopianism, which I realize is probably for the convenience of the story. But it’s worth pointing out that any real society with personal freedom and even primitive biotech is going to see an explosion of experimentation with both physical and mental modifications – enforcing a single collective decision about what to do with this technology would require a massive police state or universal mind control. Give the furries, vampire-lovers and other assorted xenophiles a few generations to chase their dreams, and you’re going to start seeing groups with distinctly non-human psychology. So even if we never meet “real” aliens, it’s quite likely that we’ll have to deal with equally strange human-descended races at some point.
I’ll also note that, as is usually the case with groups that ‘give up war’, the human response is crippled by their lack of anything resembling military preparedness. A rational but non-pacifist society would be a lot less naïve in their initial approach, and a lot more prepared for unpleasant outcomes - at a minimum they’d use courier boats to keep the exploration vessel in contact with higher command, which would let them start precautionary evacuations a lot sooner and lose far fewer people. But the tech in the story massively favors the defense, to the point that a defender who is already prepared to fracture his starline network if attacked is almost impossible to conquer (you’d need to advance faster than the defender can send warnings of your attack while maintaining perfect control over every system you’ve captured). So an armed society would have a good chance of being able to cut itself off from even massively superior aliens, while pacifists are vulnerable to surprise attacks from even fairly inferior ones.
An interesting topic, but I think you've overlooked an important sex difference on the whole "each gender goes its own way" scenario. When it comes to relationships men are generally looking for an affectionate, physically attractive sex partner, so the idea of building non-sentient (or otherwise specially engineered) companions seems plausible.
But women are primarily looking for a source of material support, preferably of high social status. This pretty much requires a partner her society considers a legal person, capable of earning money and owning property, so very few women would be happy with "catboy" substitutes regardless of how well designed they are.
Obviously the end result of this unbalance isn't going to look like the current status quo, but "each gender goes its own way" doesn't seem like a plausible outcome either.
This is a great device for illustrating how devilishly hard it is to do anything constructive with such overwhelming power, yet not be seen as taking over the world. If you give each individual whatever they want you’ve just destroyed every variety of collectivism or traditionalism on the planet , and those who valued those philosophies will curse you. If you implement any single utopian vision everyone who wanted a different one will hate you, and if you limit yourself to any minimal level of intervention everyone who wants larger benefits than you provide will be unhappy.
Really, I doubt that there is any course you can follow that won’t draw the ire of a large minority of humanity, because too many of us are emotionally committed to inflicting various conflicting forms of coercion on each other.