"Bright future" is not the same as "utopia." You can depict a future where Earth is a united world and the capital of the galaxy's largest interstellar alliance, and that's optimistic enough. You don't need to go ahead and make it a picture-perfect utopian paradise.
But since that has been established, the idea can still be workable. Earth itself can be utopia, but the rest of the galaxy can be hell. Indeed, even TNG seemed to depict this, with every Starfleet ship that wasn't the Enterprise ending up damaged and or gettng its crew killed.