I wouldn't say "needlessly obsessed with killing," especially when you consider everything about Irelia's character. She's a symbol of resistance, yes, but I never thought that peace and harmony were her thing. That's Karma. Just because Ionia has a certain culture doesn't mean they're all gonna be hippies or something. lol You can want peace and harmony but still be a warrior. They're not mutually exclusive. In fact, that's precisely why Irelia fights; she wants to protect the peace, harmony and traditions that has lasted in Ionia for generations. She is a soldier, and she's not going to show mercy to her enemies because they threaten her way of life. If you listen to more of her quotes, she has quotes that speak to inspire her allies (appropriate for a famous war leader), mourn her dead allies and only fights because the enemy picked the fight first. She's perfectly justified in being "mean" to her enemies, especially the ones who took her family away from her.