Why do we kill Yharon???

I understand why we killed that whole gods, Jungle Tyrant, Dreadon or any other boss. They all was such dicks. But why do we kill yharon? Why we have to? Like arent the gods are evil side and dragons are good side? Wasn't Yharon leave Yharim cuz he started to be corrupted? Then (if we are doubtly good guys) why we killed yharon? How lore explains this?