Long live the glorious Baku! (Spoilers)

A lot of posters here have argued the Federation has no right to relocate the Sona, because they became sovereign when they settled their "magic planet." But this overlooks the fact that the Baku do have that right!

The (conditionally) immortal Sona exiled the Baku to live out their natural lifespans and die. They apparently did this on the premise that the Sona became a legitimate government when they separated from their parent culture, and could therefore condemn their enemies to eventual death.

But then don't you have to accept that the Baku also became a legitimate government when they separated from their (literally) parent culture? If the Sona have the right to exile the Baku, stripping them of their immortality, on what grounds can the Baku not say, "We also became a sovereign people when we left to find our own way, just as you did, and we also have the right to take your immortality, just as you took ours?"