"I'm no saint, or savior. Just another sinner."
The guilt driving the Warriors Of Darkness may be similar to the guilt driving Emet-Selch, but I don't recall a point in that patch where they felt what they were doing was just, or even forgivable, and I especially don't recall the Ascians telling them the truth, that the Rejoining would not save their world at all. (The Ascians, lying? Gasp! I clutch my Ondo pearls.) Ardbert bade us to not take the path he and his friends had chosen, after we defeated them--never once did the narrative push the WoL's world and the people of it were insects without consequence. Far from it, actually. And then the Warriors Of Darkness gave themselves--again--to save both worlds.
As for the OMG story, I recall that Cid's plan to create an alternate timeline where the WoL lived was embraced by the majority, and it was only after that they acted? G'raha Tia didn't disappear from our timeline at the end of ShB because apparently the old timeline became separated from the new. (Why the Ascians in all their superiority didn't try a similar thing is likely plot convenience, but it's a nice touch, we "lessers" achieved something that they, despite their arrogance, could not.)
It's interesting to see what was done to Vauthry and his mother is tut-tutted away as "inconsequential", when their lives were just as important as any of Emet-Selch's other victims. Don't dismiss them, contemplate what was done to them fully, embrace that it was Emet-Selch who committed such an atrocity, because every other life Emet-Selch and his cronies have taken was just as important as theirs, and I am sure they are not the first to meet such an end at Ascian hands.
What happened to Emet-Selch's people was a tragedy, likely beyond anyone's control. The destruction he then inflicted on billions was fully intentional, fully avoidable, he did it without ever once feeling guilt for any of those he murdered, and he wouldn't have stopped until only those he deemed worthy were alive again. (Not ALL Ancients, mind you. Just the ones he deemed worthy.) He earned that hole we punched through him. (I'm sure he only used Varis in all those years of never telling any of his partners they were actually worthless insects he would sell to Zodiark for one corn chip. Really. I am absolutely convinced that was the first and only time. And I just know he felt bad about it! So bad, he didn't stop. He never mentioned "love" for us "lessers", by the way. The line was "I have broken bread with you, fought with you, grown ill, grown old! Sired children and yes, welcomed death's sweet embrace." "Love" was mentioned for his own people. Not us. We are breeding fodder for his machinations, at best. Do I really need to elaborate on why THAT is not "moral"? Spoiler: there's a word for THAT atrocity, and it isn't "hero".)
Emet-Selch, so heroic and righteous he needs all these attempts at whataboutism to excuse him--and it still doesn't really work! Huh. ‾\_(ツ)_/‾