Where Christian theology has Christ's teaching about government to build from and that has kept Theocratic government always transitory, Islam has a heart of theocratic law as a fundamental element. That being said, there have been vast epochs of Islamic culture where it has been able to stear clear of such Ideological simplicity and co-exist with the world in general.
The differece goes back to the point Sowell is making, that the cultural and historical setbacks make "immanitizing the transcendant" and pure utopian ideology more easyily promoted, fostered and spread within the Muslim world as a whole.
They are just simply heretics.
I would imagine the Wahabbis like Osama would want them dead also; whereas they had the chance to do God's work, but decided to spit in God's face and play footsie with the infidels.
This world isn't about being nice to infidels and getting along with non-believers. It's about doing what Allah wants done for an eternal reward. If you have doubt as to what should be done, read the Koran if you are a Muslim.