A number of years ago I was working on a novel and the unified human empire in the story were quite advanced in many ways, but their views of the other species of the world was....let's say European. The human empire had colonized their continent and wiped out two fantasy civilizations in the process; I remember having a discussion on a writing forum about the human culture and their views towards the other remaining fantasy species and people told me it's unrealistic to have people be fearful or hateful of fantasy races that had never done anything to them or harmed them in any way, even more so to be genocidal towards races that had actually showed them kindness in their hard times.
I just recently saw videos on twitter of Zionists singing about eradicating Gaza and taking the land back as though they were the victims all along (they also called it Gush Katif I think?), and in another video someone saying Lebanon would be taken as well; videos of so many Zionists saying the civilians are all to blame and are at fault as much as Hamas, videos saying the murder and worse of Israeli civilians was by the civilians and not by Hamas; I am also reminded of something I saw on a Hasan Abi video where he got a (student?) of Israeli history who talked about how the early zionists in the 1880's/1890's had been taught how to farm Palestinian lands by friendly Palestinian Arabs as they themselves did not know how to work the fields (either because Palestinian lands were different to European ones, or because perhaps they weren't farmers themselves). Today you have members of the IOF literally shooting kids and taking them hostage (and Israeli prisons where Palestinians are kept are rife with SV), and you wonder how can they engage in this behavior towards other human beings.
Of course I bring up zionism because that's the most recent horrific thing we can see where people are happily singing about genocide, but doubtless this mentality existed with the colonizers who killed the indigenous populations of Canada, America and Australia in the past. You also read quotes off wikipedia of the horrors of Cuba's Batista regime, and you see stark parallels with another quote regarding the horrific treatment of enslaved people in Haiti before the revolution.
How can you write people like this without it coming off as cartoonishly evil? It seems absurd. Reminds me of a quote, something about reality being allowed to be stranger than fiction because fiction has to make sense.