(MAJOR SPOILERS) Just beat Endwalker MSQ...

[jameseoakes]

The MSQ makes it pretty clear that the Ancients were more concerned with restoring their status quo than they were actually fixing the problem; from what I can gather, the Ancients were too used to paradise to really consider any alternatives. They seemed to have been too broken by despair to really try and make a difference - maybe "complacent" isn't the best word here - but when Venat confronted the group summoning Zodiark to try and get them to try and pick themselves up and move on, they instead went through with the summoning to try and get their old paradise back, despite that being impossible. In other words, they kept trying to focus on the past instead of looking towards the future.

Ah yes just the thing to come and do to people grieving, to telling them that they are wrong to grieve for the loved ones what a hateful thing to do. Hey everyone you loved is dead, well just get over it and move on. it's a hateful spiteful mindset.
Greif breaks people and I find the idea that if people don't react in an someone imposed way then they don't deserve to exterminated to be one of the most evil acts I've seen in Final Fantasy.