Jess is a power hungry monster, using grievances from a bygone age as his excuse to destroy the world and start over with him as ruler. The crimes of the ancestral Igratians are surely inexcusable and should never be forgotten, but at the same time the living people now are also innocent and not the same monsters who committed the sadly forgotten evils of the past.
He is the monster here for rekindling the cycle of hatred. Exacting revenge on innocents is evil and will never be the right thing to do. He wasn't even a real victim of those long ago ancient crimes, as it was from a time before he was born; he just disingenuously used it as his pretext to seize power, his moral fig leaf that he calls his "ideals".