So I peacefully acquired loads of xenos slaves through a hegemonic spiritualist star Empire. I had a species of domestic snek servants keeping all of my pops happy, I had a bunch of strong proletariat bird people (gene modded to be industrious) working on a planet of high mineral wealth providing
348 minerals on one planet, but the rest I didn't have much use for. It seemed rather rude to just purge these pops who had peacefully joined my Empire, so I set about a big relocation scheme. Habitats were constructed that were suited perfectly for their biologies (better than their homeworlds no less), and one by one they were all relocated while my citizen pops slowly took over their planets/terraformed them into gaia worlds (one notable exception to this trend being the snek servants, since they had the irradiated trait they were the most valuable colonists and spread everywhere).
Anyways after I got them all moved into their nice new habitats, I basically allowed them to do whatever they wanted with no oversight. Sure enough, they started experimenting with new philosophies, engaging in civil unrest, and before long the first slave colony declared independence. I then declared war upon this new colony of freemen (which obviously it had no chance of winning), and gave a fake surrender which ceded the rest of the colonies to this newly founded space Empire. As it is within the core of my Empire, it is safe from all predators outside my protective wings. As it possesses no starport facilities, it cannot create any warships, colony ships or even science vessels to interact with the outside world - effectively forming a curator enclave cluster. In this manner I have found a very silly way to give all of these xenos pops a paradise where they are free to pursue their intellectual pursuits without care for resources or strife, at a cost - being stuck in the self-imposed inward perfection of my Empire for all time. Given the success of this operation, I am tempted to become a fanatical collectivist, collecting all the xenos pops to put in my habitats, to keep them safe from the horrors of the galaxy :]
Helps that the galaxy in this one is pretty horrifying. I lmao'd when my peaceful hive mind neighbour turned into a devouring swarm. They went overnight from an upstanding member of the galactic community to OM NOM NOM NOM
*EDIT
Oh cool
The xenos enclaves figured can still build troop transports without spaceports, which is something I hadn't considered. Also in the time since I first wrote this post, the liberated xenos decided to form their government... As an authoritarian police state run by the proletariat xenos I put in charge. Well, that's certainly interesting, I reckon given that most of the xenos there are strong gene-modded ex-workers turned scientists, if I just turn them into a protectorate I can have a reliable source of auxiliary troops - and before long, their advanced labs will allow them to turn themselves into quite the tiny technological giant.