I've finally been shown the answer.
It's the same answer as to how there can be a Heaven when there is still a Hell.
The (first) question is, how can I be a positive, uplifting, sane worker in the pro-life movement when our sole purpose is to lobby and pray for an end to a new holocaust on the unborn?
The answer, to both questions, is that God's glory is more glorious than the deepest, darkest, horrific evil we can imagine. And I, for one, can imagine some pretty messed-up evil. Even in the presence of such wickedness, we can bask in the presence of the beautiful face of Jesus and be filled with joy.
In short, God's good beats the devil's bad.
Because the devil didn't actually create anything; he stole God's good from us and corrupted it, then sold it back to us at the cost of our souls. But God's good beats the devil's bad, and when Jesus died, he untwisted the devil's work throughout all of history, present, and future, and made it possible to receive God's good directly from him again.
That's how I can be pro-life and happy. That's how I can acknowledge that the incredible light of an unborn baby is snuffed out every six minutes in my country, and yet still know that God is good.