Zechs thought to his own past, and said calmly, "Vengeance is understandable. But it might not prevent such from happening in the future. Did you find it satisfying, enacting your revenge, or was there always more work to do?"

From someone else, that might've sounded judgemental - perhaps he still did. Or, Xue Yang might hear a thread of sympathy, such as it was. It was hard to tell with Zechs where his feelings lay, since he kept them so close to his chest.