User blog comment:FairyRaven/Fairy Tail Chapter 347: Red, Blue, Blond Hair Fight! Review and Commentary/@comment-112.205.35.163-20130816164557/@comment-7418318-20130817084638

I think that's only the case if you try to change it with magic.

Educating or convincing a bad person to be good won't magically turn another good person bad.

Same for killing a bad person. The evil of this dead person won't leave the corpse and just enter the next best good guy.