The Reasoning behind The Sundering? (*6.0 Endwalker Spoilers*)

[KageTokage]

We still don't even know if Zodiark could've actually brought back those who were sacrificed as true resurrection has repeatedly been shown as something out of reach of man and the cycle of life and death something that cannot be reversed, so sacrificing countless lives in the name of possible benefit, especially if those lives were sentient beings like the beast tribes comes across as...questionable.

The sudden shift in the Ancients' attitude of finding death in service to the star acceptable to something terrible that needed to be undone comes across to me as a likely product of Zodiark's tempering them with the selfsame desire he was summoned with; to return the world to the way it once was.

[Kordarion]

We still don't even know if Zodiark could've actually brought back those who were sacrificed as true resurrection has repeatedly been shown as something out of reach of man and the cycle of life and death something that cannot be reversed, so sacrificing countless lives in the name of possible benefit, especially if those lives were sentient beings like the beast tribes comes across as...questionable.

The sudden shift in the Ancients' attitude of finding death in service to the star acceptable to something terrible that needed to be undone comes across to me as a likely product of Zodiark's tempering them with the selfsame desire he was summoned with; to return the world to the way it once was.

The reason Zodiark could have brought back the dead was that, as we see on the moon, the souls of the ancients sacrificed to Zodiark remained within his essence. As far as I can tell they weren't trying to bring back those who died in the final days but rather were planning on sacrificing other life to replace the aether of their sacrificed brethren. Like replacing a battery but with souls and a potentially unwilling replacement.

[Cleretic]

We still don't even know if Zodiark could've actually brought back those who were sacrificed as true resurrection has repeatedly been shown as something out of reach of man and the cycle of life and death something that cannot be reversed, so sacrificing countless lives in the name of possible benefit, especially if those lives were sentient beings like the beast tribes comes across as...questionable.

The sudden shift in the Ancients' attitude of finding death in service to the star acceptable to something terrible that needed to be undone comes across to me as a likely product of Zodiark's tempering them with the selfsame desire he was summoned with; to return the world to the way it once was.

You can definitely question whether it was an influence of Zodiark or whether it was just... horrifically poor coping mechanisms. Both are equally viable.

I personally read it more as the latter. These are people insanely comfortable in their ways, who both haven't seen any meaningful hardships and have lived comfortably at the top of a status quo for ages. So when something horrible happens, they just don't have any practiced mental process on how to deal with it. This leads to them making bad decisions, because quite frankly, the right decision is way harder. And I suspect a similar reason is why they so immediately betrayed their ideals; because up until then, their ideals were easy to uphold, since they benefited from them. When things suddenly turned in such a way where their comfort and their ideals were at odds? That's even hard for modern humans to uphold, and we're used to asking ourselves those questions.