It is a very difficult topic I think

Some very early ARR spoiler










I seem the intention of Zodiark is to bring darkness and chaos to our world and he would make whole again with Hydaelyn. On the other side Hydaelyn claim Zodiark is power hungrey and banish him.
While both flooding of light or darkness mean no good for our world, and Elidibus once said Zodiark have no intention of flooding darkness to our world.

Good and evil become a simple point of view. Rejoining will result a mass genocide among all shard. However, what rejoining would bring us is never mention and while we do the deed killing every primal and extinguish darkness will result in flooding of light. Are we the good guy which our doing will result in turn our world in a form of void, or are those prepare to sacrifice all shard and bring the greater good to the one (if rejoining is actually the ultimate good ending)

We can only wait for the idea to be expand in ShB, Zodiark is inevitable