I think a United Earth would work simply because of warp drive. That would allow any element that couldn't play with the majority to leave and set up their own -ocracy elsewhere.
I'm sure by the time there is a United Earth, there Planet Talibania, Planet Kim Jong, Planet Unionist, and the like out there. By the 24th Century, they did show Planet Native American not wanting to be too tied to the Federation anymore...
"Don't try to live so wise. Don't cry 'cause you're so right.
Don't dry with fakes or fears, 'Cause you will hate yourself in the end."
Anime @ MyReviewer