Krauthammer lays down the stakes:
This planet has been around for 4 billion years, intelligent life for perhaps 200,000, weapons of mass destruction for less than 100. A hundred--in the eye of the universe, less than a blink. And yet we already find ourselves on the brink. What are the odds that our species will manage to contain this awful knowledge without self-destruction--not for a billion years or a million or even a thousand, but just through the lifetime of our children?
That is why we're at war. Not imperialism, not glory, not conquest, not oil. Everything decent about humanity is threatened by everything wrong with us. We can't afford to lose, we can't afford not to fight.
(Found by Moe Freedman.)