No wonder the Black Mage wanted to see the world in ruins. To be hated by everyone, and to have his only source of happiness forcefully taken from him, it's no surprise that Arman had lost any sense of semblance and went crazy. Iris didn't want to justify the Black Mage's sins, but she didn't think anyone could easily get over the fact that your own family was murdered behind your back.
Since Kieran had said that Arman was already a powerful mage by then, he must have borne a great regret and guilt for not being able to protect them. Being a magus herself, Iris also knew the feeling of being useless when it comes to protecting her friends.
"I didn't mean to make you upset, Iris." Lord Kieran said, looking at her worriedly. "But this truly happened, and while I understand his pain, I cannot condone his murderous actions towards innocent ones."
