Here's the real question: In what way is Emet-Selch wrong?
Consider the following:
- Humanity has never needed Ascian help to spawn wars. Most of the wars that have occurred on the Source were actually not the work of Ascians. Granted, they are always there in the background, but there have been plenty of known instances where people were quite willing to do the deed without the need for prodding from higher beings.
- Emet-Selch may not be wrong in treating current humanity as little more than gnats. The races that were created by the sundering haven't actually evolved at all from the get-go. Sure, they've adapted to new environments and come up with some interesting technology, but their aetheric and physical capabilities remain largely unchanged. Even most of their actual advanced technology--i.e. that which was/is employed by the Allagan and Garlean Empires, respectively--is at least partially a result of Ascian assistance.
- Consider the Ascian view. They are in effect literal gods that can do virtually anything they want - even reshape reality to suit their ends. An Ascian dealing with an ordinary hyur is about the equivalent of a real life human dealing with a lone fire ant that decided to sting them.
- Would the Rejoining be that bad? Probably not. People would be whole again, their original memories and identities restored. They would be free to live in a star-spanning Utopian society where concepts such as violence, vagrancy, destitution, hunger, sickness, and pain no longer have any presence or meaning. Everyone would exist in a state of parity, free to live out their lives joyfully creating whatever their hearts desire with their newfound (or technically newly restored) powers of creation.
- Is it truly wrong for someone to seek to regain so many things that were, at least from their perspective, unfairly taken away? To Emet-Selch, everything he sees serves as a constant reminder of what was lost when Hydaelyn smote Zodiark.