[6.0 - 6.4 Spoilers] An interesting video detailing Venat's polarizing reception

[Cleretic]

Literally in UT they beat your head in with the fact that even if a society is doomed to fail it should be on their terms and let them be, not to further expedite the process.

And should that society not have input on their own fate?

The core difference between the Ancients and the societies of Ultima Thule is that most of Ultima Thule's fallen civilizations were due to outside impact; the dragons got hit by the Omicrons, the Grebuloffs fell to disease, the Karellians and Nibirun started their slides based on the influence of Meteion. The exceptions to this are the Ea and Omicrons, where debatably the crisis for both come from the fact that they didn't fall, they're both essentially gripped with crises of existential dread and 'what do we do now'.

The Ancients, meanwhile, fell to the Ancients. In fact, in all three of their possible endings, the fault lands at their own feet. Going in order of the times things spring up:
1. If for whatever reason they didn't come up with Zodiark, they would've died to the Final Days, which is pretty squarely Hermes' fault, although certainly Ancient society isn't entirely without blame.
2. If Hydaelyn didn't step on up to the plate, then everything we've been told would suggest that eventually they sacrifice the planet dry for Zodiark. This is more a societal thing, but if you want to put a face to this side, I'd personally say Elidibus.
3. And for what did happen, Hydaelyn leg-dropped from the top rope, leading to the Sundering. Venat's hands are the ones bloodied by this, clearly.

I would argue that the reason Venat comes off as 'the one villain' of this particular micro-story to some (which I think is a gross oversimplification of said micro-story, I'd say there's no villains in it) isn't because she's the only one with a gun, it's because she's the only one that landed her shot. Everyone else is only guilty of attempted murder, she managed to knock the 'attempted' off the crime list.

But something that must also be remembered is that her plan was the only one that would've left survivors. The End of Days would've wiped out the whole planet if not stopped (as evidenced by, weirdly, Hildibrand), and Zodiark sacrifices would've rendered the planet bone dry (as evidenced from the Nibirun). But the Sundering, (as evidenced by everything before Elpis and most of what's after it) didn't just leave a planet full of people, it left fourteen planets full of people, albeit mostly different people. That hardly makes her objectively morally right, but from an omniscient readers' perspective surely we can see that her decision the kindest and most ultimately fruitful out of all options.

While you are certainly allowed to disagree with her, Venat is not a villain. And to call her one requires brutally simplifying that part of the story in the single-minded pursuit to declare there to be one in the first place.