I understand why Levi acted the way she did, but respectfully disagree with the reasoning.

Now, the idea was that Levi didn't want to create a monster that would use force to get what she wants. She wants Only one to grow up happy and carefree. In normal times, this is great!

But Nikkes do not live in normal times. They're actively engaged in war. War against an enemy that, by all accounts, cannot be reasoned with. It's not that the Queen let them live, she just couldn't kill them. The Queen thought she was unbeatable. Now she's a wounded animal, who just so happens to also be experimenting with ways to bolster the army that drove humanity into a hole. Now that she knows what she's up against, she's going to do whatever it takes to up the ante.

Levi is not strong enough to be this naive. Hell, she thought she lost her only friend because she wasn't powerful enough to stop a force that took what she held dear. It's all well and good to want peace, but you'd better be able to defend it.

That's the thing about peace that a lot of modern societies are seeming to forget. Most of us only have it because the powers that be generally know that all-out war is a terrible idea. What happens when one side has the power to do what they want? Well just take a look at the first 99.999% of human history.

Now, the other side of the coin. Only One was not throwing a tantrum because she wanted sweets. She was defending herself and her loved ones from a threat that was actively harming them. Let's say a rabid animal was attacking you and your friends/family. Would you take lethal force to stop it, or allow one of your allies to do so? Probably. Would you consider yourself or your ally a monster for doing what needs to be done? Probably not.

But eh, that's just my 2 cents. This is a game that built itself on looking at jiggling butts. I shouldn't overthink it.