Theocratic states are, by definition, not rational. Stalinist Russia, Fascist Germany, Mao's China, Kim's Korea, Revolutionary Iran -- they all believed God or History would preserve them against all odds.
Israel and America aren't theocratic states, but both nations have a strong strain of theocracy. In the US that strain is concentrated in the GOP. A belief that God is on your side can lead to some otherwise inexplicable and irrationally self-destructive behaviors.
I don't think the US will default - but we are rather close to the edge. We need to understand not only how the GOP got to crazy, but why. Why does a significant portion of the GOP believe that America should do this?
For many Republicans it's their version of Mao, Marx and Mohamed. They are American Marketarians, believers in a peculiar 21st century American fusion of Christian fundamentalism, evangelical capitalism, and calvinism. They believe they are doing God's will, that progressive taxation is the greatest sin -- opposing God's will and justice. They believe that God will save America -- if America follows the true course. Even if they don't personally believe that Obama is the anti-christ, they know he is not a Believer.
They can't make a deal, because they'd be denying God.
That's why we're in trouble.