Some people who are raised or inducted into that ideology do get out of it. More than enough stories out there about people who realized it was all bs and regret having ever believed in it. I also have read the author's other works and I think it's far more likely that this story ends with the...
So I have a theory with the latest chapters. I think the previous demon lord is Iruma's father and he left the demon world for the human one. His mom is human and Iruma is half demon half human.