The Doctor and Bonnie in “The Zygon Inversion”

You just want cruelty to beget cruelty! You're not superior to people who were cruel to you, you're just a whole bunch of new, cruel people. A whole bunch of new, cruel people being cruel to some other people, who'll end up being cruel to you! The only way anyone can live in peace is if they're prepared to forgive. Why don't you break the cycle?

Why should we?

What is it that you actually want?

War.

Ah. Ah, right. And when this war is over, when you have a homeland free from humans, what do you think it's going to be like? Do you know? Have you thought about it? Have you given it any consideration? Because you're very close to getting what you want! What's it going to be like? Paint me a picture. Are you going to live in houses? Do you want people to go to work? Will there be holidays? Oh! Will there be music? Do you think people will be allowed to play the violin? Who's going to make the violins? Well? Oh, you don't actually know, do you? Because, like every tantruming child in history, Bonnie, you don't actually know what you want! So let me ask you a question about this brave new world of yours. When you've killed all the bad guys and when it's all perfect and just and fair, when you have finally got it exactly the way you want it, what are you going to do with the people like you? The troublemakers? How are you going to protect your glorious revolution… from the next one?

We'll win.

Oh, will you? Well, maybe. Maybe you will win! But nobody wins for long. The wheel just keeps turning. So come on. Break the cycle.