And the big problem is that regarding the Plenty, she had a summary of a couple of lines of what happened to that star. She had little reason at that point to attribute it to "apathy towards life" as such (which does not appear to have been the ancients' view tbh, nor were they lacking for emotions), but rather apathy towards it because joy became meaningless in the absence of sorrow. The problem people have here is how she is connecting this to her people outside of that singular cutscene - bearing in mind not all of us have suffered amnesia regarding the events of SHB and their recounting of events leading to her faction's summoning of Hydaelyn. It is possible that, one day, they too would meet that fate - it's possible they might not. The issue is that the scene in question shows her sundering the star at a point where her people are still mourning the loss they suffered, of the state of their beautiful star, to which they were devoted. And the problem people have with that is that they were not given the necessary information as to what she was basing her concerns on, as opposed to being provided rather glib platitudes when they express a desire to reclaim their former way of life. So her people were never really given a proper opportunity to consider it and make adjustments if necessary, once a proper understanding had been achieved. So for Ms "Nothing is impossible", apparently a conversation with her people about what Hermes had learnt via the Meteia was too difficult. There may be logic there that would make sense to her or Hermes with the knowledge they'd acquired, but not so much anyone else. Hermes's own mindset was to foster life even when it became inimical to the broader balance of the star. He is not exactly reasonable.
It goes beyond that even, because the dragons had attained something like a state of perfection and their star's destruction was not due to the incoherence of such a society but for no other reason than it was invaded by the Omicrons. Stars mired in suffering perished, those without it perished, those anywhere in between perished. So there's that. A fate that may befall the Source too, in any case, in the future, once the "lessons" the Scions supposedly learnt are gone. The poster here made a good list of all the issues with her thinking.
What she did makes sense to her, maybe. Not to anyone asking well why not give your people this knowledge to give them a chance to adapt, rather than just mouthing off some platitudes about suffering that in the moment, seem vacuous?
If you consider it reasonable to sunder your own people, based on a half-baked understanding of what happened to another star, which you never even tried to explain properly to your people, based on what was shown so far, then so be it... I certainly don't.