so now i think i can say that sensei has the ability to write peoples stories, and to help correct their story in a pleasant way. also he got the plot armor he doesn't want. just like a certain muffin
Of course they became villains, they were at first unstable people that were in depression, got into another world and obtained OP power with no one there to punish them when they do bad stuff
Maybe some otherworlders are good guys, but most would become bad guys in this situation, especially the main heroes who would want a reward out of killing the Demon Lord