Ah, but they have him back story and motivation.

Spoiler warning: He wasn’t purely evil for evil"s sake, he just tried to rebuild society for the scions of humanity, and had already discarded the normies (can’t remember the term they used) as primitive, albeit barbaric, creatures.

The genius of Bester is that he was so self assured and uncontested, making him almost cartoonishly evil, but also that he was so essentially human. Driving home the major themes of the series: the dangers of unchecked power, the human drive to self determination, and that wielding power over others perpetuates a cycle of violence.