I don't have a solution to states becoming tyrannical. Things that exist for other purposes eventually evolve to behave in a way that is self-serving. This is why political parties don't actually make political progress. All the power of the party eventually gets spent maintaining the power of the party. Any party that doesn't play that game falls out of power and disappears.

Same with unions. They now exist to maintain the union and any benefit they give to workers is only a side-effect of maintaining power.

This happens with species as well they exist to maintain their lineage. Only humans have gone through enough game theory to develop altruism as the next tier of evolutionary advantage. That step is still incomplete. Governments as a higher layer organism are still behaving like brutes. I am not sure how long it will take for states to evolve a sense of selflessness. Maybe a million years? Until then we need to iterate.

The trouble is that earth is only big enough for a few hundred governments, they become old and brutish and people suffer under their thumbs. To the stars!