*Spoilers* Anyone feel joining Emet would have been better

[KariTheFox]

Because they were all dead and the world was a ruined wasteland by then.

Was it? It's my understanding that the blasphemies were something that affected sapient beings, who have the capacity to despair. And they'e not animals, they don't hunt or eat. They only want to spread further pain and suffering. The rest of the biosphere, animals that have no capacity to feel that kind of existential dread, really don't seem to be affected at all. But I could be wrong.

Besides, I think that misses the point. Zodiark isn't an engine you can just throw biomass at until it does what you want. The ancients were sacrificing themselves to zodiark in a religious manner, because "sacrifice" implies giving up something of value. In the case of the ancients, the lives of their beloved brethren, and the chance to ever return to the aetherial sea and be reborn to the star. Things highly valued in their culture. It's a sacrifice because the loss was keenly felt by everyone involved.

But a bunch of non-sapient animals? To the ancients - able to create anything, who wanted for nothing? How would it be a meaningful sacrifice at all to round up a bunch of animals and kill them for zodiark? It would be effortless, and they would be able to recreate everything they "sacrificed" easily. It's not really a sacrifice at all, it's more like a biomass delivery.

[Veloran]

Was it?

Yes, all life and the Lifestream itself was being killed. This isn't exactly consistent with what we see in Endwalker, but it was their situation then. The devastation was probably exacerbated as well due to the Ancient's creation magicks being hijacked, creating things like endless rains of fire and tidal waves engulfing the land. Regardless, by the end we're told the planet was completely ravaged and all but lifeless, which is what led to the second sacrifice to restore it and restart the Lifestream.

Besides, I think that misses the point. Zodiark isn't an engine you can just throw biomass at until it does what you want.

That is in fact exactly what Zodiark is. He needed massive amounts of aether to do the massive things they asked of him, and the Ancients were the biggest (and at that time only) reservoirs of aether around. This metaphysical, religious aspect you describe, where they needed to give up something intangible or spiritually important, is not part of the equation. It's very much true that they revered Zodiark given he was their only hope, but where you got the rest of this idea I have no clue.