I love the Dalek because they never, ever stop: they only want to kill. They're what happens when you draw the line from mercy to justice and out into the dark places. But that unity, that scarce feeling, that darkness: that came from Davros. That's what his soul is like. And the Doctor? I love the Companions, I love you, because you never, ever stop: you only want to save the world. What happens when you draw the line from innocence to experience, and on into grace? No contest.
Of course, what's better than a metaphor is the real thing. On the planet of the Hath the Doctor had another daughter. A new daughter, Genny. She reminded him of everything he'd lost -- Gallifrey, the Academy, family -- and everything he feared about himself. War. The scars and madness of the war were implicit in her, and they were radiant. Down to the five thousandth generation. It was a paradox that you were there at all, Donna: the TARDIS brought you and Martha with him to the planet before Genny ever existed. But if you hadn't come, she never would have. This is the way a Time Lady should be born.
But this is no ordinary war, of course. She's not an ordinary soldier, in an ordinary war. Five thousand generations, in seven days... How would that look to a Time Lord? How do we look? Five thousand human generations, all those infinite stories: hard to remember how long it takes, for us. Even harder for the children of the machine: "I have a body, I have a mind, I have independent thought. How am I not real? What makes you better than me?" That was all she had to say, for you to love her.
"If you really wanted peace, couldn't you just stop fighting?" Spoken like a God. "I'm trying to stop the fighting."
"Isn't every soldier?" Spoken like a human. Spoken like every Companion that ever walked those halls, or heard those heartbeats.
Of course, this is only a story, so he turned out to be right: in the muck and the filth and the stinking baseless hatred, there was beauty: a mistaken myth, a story about life and time, was forgotten. You helped him uncover it, and a world was born. You thought all the buildings were in ruins -- that time, and life, had passed you by -- but they were only empty, and good as new. Waiting to be populated.
They'd mythologized their entire history, until it was all they thought they were. And oh, you sympathized, didn't you? Totting up your facts and figures, discerning where it all went wrong. Exactly the moment they forgot the breath of God, and turned upon themselves: you could calculate it to the day. They could have turned left, but instead they turned right. They lessened their punishment, but didn't forgive their crime. They fought a war for clemency, instead of redemption.