On Hykkan Prime, a newly colonised planet in the far reaches of the Interstellar Seelee Directorate, some Seeleelee (that’s my weird plural form for the species) are not happy. They had recently migrated to the planet, an arctic world suitable to their biological make-up, from elsewhere in the empire, because they were not happy. But now they’re still not happy. The reason is that the Interstellar Seelee Directorate allows alien species to vote, and allows them to be governors, scientists, and admirals. Worst of all is that along with them, several groups of alien Vool have also migrated to Hykkan Prime. These Seeleelee are not happy. Because they are xenophobes.
In Stellaris, you create or pick a starting empire along with a species. While the species has certain biological traits — such as being adaptive to hostile environments or having below-average lifespans — they also have a more mutable set of ethics. They start with a particular ethos, but depending on circumstances, members of the population my deviate from it. To start with, the Seeleelee were xenophiles and fanatic materialists. In the game’s terms, that means they are hard workers and avid scientists, are quicker to trust other empires once friendly relations are established, and are happier on planets with intelligent species diversity.
However, once the empire starts colonising empty planets in the galaxy, populations can diverge ethically. Seeleelee on new planets can develop an ethos of their own that is not compatible with that of the empire as a whole. The Interstellar Seelee Directorate allows free migration between planets for all species, which means that unhappy Seeleelee are free to move to new worlds if they are unhappy in their current situation. In the Directorate, the xenophobes are almost always on the move, migrating to a new colony as soon as it is established. However, the Directorate has migration treaties with numerous other empires, which means that Vool, Steccashi, Teldarans are constantly moving to new and existing colonies as well. It appears the Xenophobes are never free from living with aliens, much to their chagrin.
Apparently, the xenophobic Seeleelee are not so unhappy as to revolt. Some of them have organised into secessionist factions, but their support is marginal, since most Seeleelee (and alien immigrants) are xenophiles. In addition, the government actively suppresses such factions. In theory, they would be free to move to other empires, but they would still be living among aliens, and the empires that have a migration treaty with the Directorate are also predominantly xenophilic. There are other xenophobic species and empires, whose ethics on migration and slavery would fit the Seeleelee xenophobes perfectly. But of course those empires would never dream of allowing a filthy Seelee to pass their borders, let alone immigrate! And so the xenophobic Seeleelee are unhappy, moving from world to world in the hope of finding one where they can be alone with their xenophobe buddies and grumble about the empire’s voting and migration policies.
Ironically, the least unhappy are the xenophobic Seeleelee who live back on the homeworld. Sure, they find the government distasteful, but at least there are no aliens living on Uraya, since they never migrated there. Make of that what you will.