The universe can’t be dominated by one force both have to exist or everything becomes a living hell. A blinding world where everyone is in perpetual agony or a dark world where nothing moves. If we are to truly get rid of the darkness we’ll also have to get rid of the light, something Bungie hunter at in year one with the Symmetry flight ship.
-
There’s a Drifter / Emissary dialogue which indicates the need for Light and Dark to co-exist