So starting from the beginning, in ShB we hear from Emet that they summoned Zodiark to stop the Final Days, he/ it succeeded, and that there were some people who feared his power who eventually summoned Hydaelyn in response to keep him in check. They fought, Hydaelyn struck a single blow that wound up causing the Sundering - though it remains ambiguous as to how intentional it was - and later on we learn from phantom Hythlodaeus about the sacrifice required to bring Zodiark into being, how they wanted to offer up the new life in return for the lives lost in the sacrifice, and that the faction who brought Hydaelyn into being disagreed with this and it served as the motivation for her summoning.
At this stage, it's acknowledged that what happened to the Ascians and their people was tragic even in light of this disagreement and we sympathise with Emet's pain, but ultimately we can't condone his actions and allow the Ascians to continue, because murder is wrong, we also deserve to live, and it's not up to him to decide who will live and who will die. It's also inferred there was more going on behind the scenes that Emet remains wilfully ignorant of relating to the power/ influence Zodiark exerted and the fact of their tempering, and that there was a reason the situation was untenable and made the summoning of Hydaelyn a necessity, and the Sundering an unfortunate but feasibly unintended outcome. Cool.
Enter EW. We lose the angle of the Convocation and/ or Zodiark being the pivotal problem as well as the issue of the sacrifices, and it becomes purely a matter of their suitability in weathering the Final Days. We learn that Venat knew everything all along, and what we told her guided her actions and triggered the events ShB first revealed. And this is where it falls apart.
First of all, any sort of moral high ground Venat may have had over the Ascians that justified her position is now gone, because the minute she knew what the consequences of her actions entailed, what followed was no longer about concern for the preservation of life. She loses that argument after she consciously chose to sacrifice everything along with the Ancients in the Sundering to allow for the future where we exist. The new life wound up dead along with all the rest of them.
In an attempt to maintain it, the argument becomes "well, they couldn't handle despair, so they wouldn't have been able to defeat Meteion, and they needed to die to make way for the humans that could." But the problem here is that the mortals succeeding is not actually a given outcome - she even comes up with a contingency plan in the event we fail - nor is it a particularly fair comparison, when we have the benefit of prior knowledge and insight into the phenomenon because of what they went through. This is just a judgement Venat makes herself. She is given the information about what will come to pass, including the murders perpetuated by the Ascians as a result of the Sundering as well as the tragedy of the Sundering itself, she is crucially told what the Ancients never had access to in having knowledge of the true cause behind the Final Days and how to combat it, and she is left with a choice: to either believe in her own people, offer them vital information and see if she can prevent any of these events coming to pass, or going through with it and believing in us instead. And she chooses the latter. She chooses to throw her chips in with our lot, believing we are the best hope for mankind, which is meant to be very heartening and moving, but obscures the fact that in so doing not only is she making a choice here of who gets to live (and try) and who dies, and depriving the Ancients of the agency to self-determine their fate, (regardless of the outcome) - which was the very reason we fought Emet in ShB in the first place - and of the knowledge that might help spare them further, but she decides that everything the Ascians did, including the deaths of the victims of their actions, is necessary to make that happen. When the idea that "X needs to die to make future Y come to pass" is exactly the same judgement the Ascians made that they are so frequently condemned them for, only the difference here is that it is framed positively, in that she has been inspired by the WoL and chosen to place her faith in us. But that doesn't change the fact that the crux of it is that she has judged us more worthy of life in this instance, and we allow it because it preserves our future. And through this decision, the sum of her sacrifices actually winds up greater than theirs, because of the accumulative collateral damage needed to get to that future in the first place in terms of the Ancients, the new life, the seven shards and all of their inhabitants, and the victims of the Calamities. She knew all of this was the price to pay for the judgement she made, and she said "okay."
So basically the Ascians killed the Sundered, and said "we choose our people. You are not good enough to be entrusted with the fate of this star." And we criticised them for that, and we fought them believing in every living being's right to life and the ability to decide their own future.
Venat killed the Ancients, the supposedly all-important new life, allowed these other murders to go on unchecked because she needed them to happen, and said, "I choose these people. You are not good enough to be entrusted with the fate of this star." But for some reason this is seen as right, and her character viewed as wise, benevolent and kind. And this is what people are arguing against; neither side is right here, but fighting for their own corner, with Venat's decision actually having the edge on whose choices resulted in the greater number of sacrifices. To which other people say, well, Venat being seen positively is what the writers clearly intended, so it must be right, and the judgements and perceptions of the characters are correct because the writing said so, and you wind up with two different points of view duking it out on the forums for two years, when really it all comes down to a case of bad writing as a result of rewriting and cutting large chunks of an entire story at the last minute and trying to be deep and philosophical without sufficiently exploring the themes involved or providing adequate set-up to allow that to happen and feel genuine and meaningful - but not everyone wants to see or consider that, and this is where the duking it out gets personal and very heated. Whereas if this had simply stayed an issue between the two sides with no interference on our part, it all would have remained an unfortunate tragedy of clashing ideals, with Venat and her belief in the value of life giving her the moral victory over the Convocation, and leading to the natural outcome of her assuming stewardship over the newly-Sundered life after the fact and doing her best to nurture and protect them against the Ascians, which keeps her framed in a consistent, positive light and renders the rejoinings and such a sad fact of reality that she tried to prevent. Or, to put it more simply, a coherent story. Which is all most people here actually wanted, really. But apparently that just wasn't "good enough."