dante's actions (existence) caused an uproar that violently shook the earth and even though he wasn't trying to, he was causing terror by living. nephilim are evil things to demons. sort of how al qaeda is america's main threat, even if they stop attacking us, we will try to hunt them down and kill them all, sort of like what mundus did to the nephilim. if you're with al qaeda and not involved in or even interested in harming americans you're still an enemy because you have the potential to cause another 9-11, just as if you are nephilim, even if "you don't give a ****" you still pose a danger to the demons because you have the potential to kill the demon king.