Think it’s more of what they would and can do if they wanted to without morals.? Thinking that if push come to shove humans are selfish. Lwk ig is nonsense since they art acting like that but the mermaids were discriminated against and treated much less then a animal by the people there with only one person who ever treated them kindly killed by his own kind.
Their belief wasnt shatter overnight but grew slowly and like mess with them mentally. They were doing anything possible to bring ‘him’ back, and extermination is the only way they know I suppose??? Like what can they do? Beg the sun god?????? and they are not humans fundamentally they have different views and way they think. The child was simply overwhelmed with hate and missing the one person who treated him like family? While idk about the older sister. Think she experience way more and lost hope in humanity. They have NOT meet anyone else who are kind I think. Only gio(?) cuz like they are still stuck with the him thats gone and it's haunting them.
Medieval times are scary. We as humans back then not even that long ago did horrible things jusy cuz someone of our race is bit different. I don’t agree with what the mermaids did but I wouldn’t say it's like a dumb argument? Dunno.
They simply think all humans are selfish and cruel except Thier teacher, they even hate the sun god for not saving Jio, they're destroying the dimensions out of rage for humans and as revenge against the sun god too (i don't think they ever felt faith for the sun god, they had faith in Jio himself).
And I don't think they know, or rather, believe that good humans exists, they never spent time with other humans exept jio, the little boy only had to pretend to ba a human this time because they found some difficulty in attacking this dimensions right after finding it, so for them, only jio is good, because they only experienced his kindness, and honestly he sets the bar very high to be as kind as him, even at the moment where humans fed him to his student, he didn't showany hate towards them or towards the boy while he was getting eaten alive. Who can match that?! If it was me I'll feel so much hate for other humans and be scared of mermaids because of the trauma

What do you mean human surpass limits with cruelty? You guys literally attack one race and experiment on them despite knowing the existence of good people. I hate alk this 'humanity ' this, that, as if creatures that criticize is different. Thats the thing about free will. There will be horrible people, so will be good ones. Such a dump arguement. Anyway, Ji wakes up, your husband needs you