Read through this thread, and the thoughts on what Venat did and whether she was justified...

I have to admit, after seeing the story play out, I was not convinced that Venat did the right thing. Her decision to withhold information and try to guide her people to saving themselves, even with the foreknowledge that this DIDN'T WORK, seemed nonsensical. At the very least, she should have shared what she knew about Metion once it became clear that things were falling apart. Even if everything worked out in the end, even if the actions taken eventually resulted in the defeat of Metion (something the Ancients might possibly never have been able to do themselves; the best they could manage was shield themselves from her influence), I was not convinced that Venat might have done a better job if she'd shared her hidden knowledge with her people, just as we chose to share our hidden knowledge of the future with her and the others.

That said, I seriously think there's an aspect of Blue and Orange morality going on here that has to be taken into consideration. Hermes was sad. He was sad because the other Ancients couldn't seem to understand that their creations could suffer, that they could fear death, that they could feel pain. Eventually, he enacted his memory erasure plan to ensure that the Ancients themselves would eventually face a trial to decide whether they were fit for survival.

I think there can be little doubt that the Ancients held themselves as being a tier apart from their creations, above them and fundamentally superior and of greater intrinsic importance. Certainly, they might favor such creations, bear affection for them - but that affection is much like the affection that we have for pets, even in cases where the creations are clearly intelligent beings. Several of the Elpis quests made it quite clear that even intelligent creations were seen as disposable and replaceable (such as the quest where we're instructed to allow the beast to rip us apart if it became a choice between its life and ours - it's an important research specimen, after all, and we're just a familiar!).

More than that, though, there were some strong hints that the Ancients did not hold their OWN lives in especially high regard, either. It's a regular occurrence, for instance, for an Ancient to simply decide that they've done enough and that it is time to die. Half of all the Ancients decided to sacrifice their own lives to birth Zodiark, and while that seems like a breathtaking spectacle of altruism from our perspective, to the Ancients it might not have been quite so unimaginable.

As another being from this culture in which Life - both that of the Ancients and not - is considered to be ultimately not that important, Venat's decision becomes a bit more understandable, even if it seems monstrous to us. She held back from spilling the beans regarding her future knowledge specifically because she was willing to allow Hermes's experiment to play out, to see if they would be able to prove themselves worthy of continuing to exist on the planet. It was a test which, in her estimation, they failed, as their solution was to hide behind Zodiark and ignore the underlying problem - and further, to hypocritically destroy the creations in which they'd claimed to have placed so much importance, simply to bring back their lost brethren. Where did their high-and-mighty ideals about maintaining ecological balance on the planet go once their collective back was to the wall?

This irreverence for the value of life was both what allowed Venat to do as she did, and also what prevented the Convocation and the rest of the Ancients from finding a lasting solution. The same irreverence for life is quite likely what would have lead the Ancients to their eventual doom - possibly one similar to that of the third leg of the Dead Ends, a world so utterly free of strife that its people had lost all meaning to their existence and any will to live. It was time to allow a new people to step up to bat.

The Sundering resulted in life forms whose existences were brutish, painful, and short. Life is fleeting and precious, and the living claw and scrape for as much of it as they can. Carelessness for life like that displayed by the Ancients, both in regards to their creations and to themselves, is regarded as abhorrent. While by no means guaranteed, this new form of life had a chance to overcome the tests that had laid every other galactic civilization low - and so far, they have.

tl;dr, it's hard to swallow what Venat did, when looking at it from our own perspective. The game, however, paints Venat as being from a culture where such an abominable act might not be quite so abominable.