The villains, (SEELE) a secret organization who secretly control world governments, want to fuse all humans in to one to bring back their satanic god.
Now look at whats happening. They want to fuse men and women with transgenderism and nonbinary shit, they want to fuse countries and remove borders and create a one world government and they want to fuse races with race mixing.
I find your original theory lacking to be quite honest.
I find the UP3 theory from Star Ocean series to be more convincing. Advanced star faring civilizations choose to not make contact with less advanced civilizations in order to preserve their authentic development.
If humans manage to reach out to galactic federation then that means they meaningfully united on their planet and pulled all their resources for a single unified purpose and devised methods unique to them to do so.
If humans wont manage to reach out to galactic federation then that means there's no point in bringing them into the galactic forum as whatever that is dividing and stalling human progress would likely affect the greater galactic society as well.
Most likely, aliens don't exist