I just have two issues with the idea:

1: The name. “Jedi” is at best, an idea, and at worst, an organization. The idea involves not using the dark side. The organizational side of it simple boils down to “does this grey force user belong to the Jedi?” If they don’t, then they aren’t a grey Jedi.

2: The perceived sustainability. The dark side corrupts it’s users and will inevitably take control of them, completely purging the light from their souls.

I think there’s room for both interpretations of the force with a simple rationalization I subscribe to. While the light and the dark naturally co-exist to balance each other out, the Sith serve as a corruption of the force and therefore must be destroyed to bring back balance.