It's not clear if the Baku even thought of the planet as theirs.
They just called it "home" because they're quirky.
And see: Palatine and Israel.
It is much more like the episode Ensigns of Command.
No it's not.
it was a humanitarian move.
In what twisted world is kidnapping "humane"?
The humane thing would have been to turn around and go home.
You're essentially trying to excuse a large force's persecution, subjugation and displacement of a smaller one to gain access to a natural resource. As a society, we don't do that. As a matter of fact, we tend to condemn it.
Trying to justify it by invoking some bastardized interpretation of the Bentham Pannomion holds about as much water as a thimble. Utilitarianism has its place; implying one's claim to absolute power is more significant and essential to anther's by simple arithmetic is not it, especially under the guise of "health benefits."