Islam is a syncretist religion that took a bit of paganism (the moon good, violence, etc.), a bit of Judaism (parts of Mosaic law and the more politically aggressive scriptures that suited its innately aggressive reach), and a bit of Christianity (proselytism rather than birth being the membership mechanism) and created a truly hellish mixture out of it.
Even by the time of Jesus, Jews had stopped following some of the more radical urgings of the OT, and they had built up an entire lawyerly class to show them how to manage the apparent contradictions. In addition, the fact that Rome held the secular power obviously made them more predisposed to a division between religious law and secular law, which was something essentially formalized by Jesus (render unto Caesar, etc.).
The problem is that the bizarre conglomerate that forms the Koran takes many of the most obscure bits of all of these,complicated by the fact that Mohammed installed an essentially hereditary structure (this is, after all, what gives the Saudis such power among Muslims), combined it with conversion by violence, and then gave the decision making power to a bunch of crazed clerics who were also earthly rulers.
Really, the only way that Islam works is in the societies that ignore it.