Religious fanaticism!

"In our own day the Christian mission encounters religious intolerance in many parts of the world, but it is found in its most virulent form in Islam--the most fanatical of all religions. As mentioned before, in Islam there is the Law of Apostasy which permits the community to kill any member who defects from the faith. This law goes a long way toward accounting for the paucity of converts from Islam. The law is not always applied, but its very existence acts as a strong deterrent. In most Muslim countries conversion is an exceedingly dangerous undertaking and only the bravest souls have the requisite courage to face the prospect. Discipleship is so very costly that few are willing to pay the price. A veteran missionary to the Middle East had this to say: 'So confined is the Muslim that in some countries of the Middle East a follower of Islam who changed his religion would in effect be tearing up his birth certificate, citizenship papers, or passport, voting registration, and work permit; and would become like a man without a country.'" from Christian Missions in Biblical Perspective by J Herbert Kane pages 278-279