I was replaying DMC 1 again and i have a really different look on him now. It all started because Sparda and Eva, a Demon and Human fell in love forming a union between two entirely different beings. Demons and Human just arent meant to be together as they literally belong in different realms. Yes the two were in love, but look as Mundus point of view. Clearly he is the ruler of the underworld, nothing is more important than making sure that the underworld remains as it is, and nothing happens to it. In his eyes Humans and Demons should not be together, and if you think about it hes kind of right. The Humans and Demons were at war in the past so apparently something had to of happened. Something so terrible that Mundus felt it would be better if the humans just didnt exist anymore. I really wish we got some more insight on this because it would really be awesome if they did show it.