"People of the Book are not considered infidels in the Koran. So, which infidels do you refer to?"
True. And it should also be noted that Muslim clergy far more often tend to issue fatwahs (religious rulings) against other *Muslims* who have blasphemed against Allah, than they do against non-Muslims.
And as for the Bible saying "Thou shalt not kill", the passage is more often (and properly) translated as "Thou shalt not murder". There is a difference between killing and murder, as any soldier knows. In addition, this poor world has seen more than its share of Christian soldiers marching onward into battle, whether it be the Crusades of the past, or the Christian Right's overwhelming support of the death penalty today.