It is also worth understanding why Qaradawi says Islam and secularism cannot co-exist. The excerpt from his book continues:
As Islam is a comprehensive system of worship (Ibadah) and legislation (Shari’ah), the acceptance of secularism means abandonment of Shari’ah, a denial of the divine guidance and a rejection of Allah’s injunctions. It is indeed a false claim that Shari’ah is not proper to the requirements of the present age. The acceptance of a legislation formulated by humans means a preference of the humans’ limited knowledge and experiences to the divine guidance: “Say! Do you know better than Allah?” (Qur’an, 2:140) For this reason, the call for secularism among Muslims is atheism and a rejection of Islam. Its acceptance as a basis for rule in place of Shari’ah is downright apostasy.
Apostasy is an explosive accusation. On another occasion, Sheikh Qaradawi explained that “Muslim jurists are unanimous that apostates must be punished.” He further acknowledged that the consensus view of these jurists, including the principal schools of both Sunni and Shiite jurisprudence, is “that apostates must be executed.
If we were in that objective frame of mind, we would easily see that a freedom culture requires separation of the spiritual from the secular. We would also see that sharia — with dictates that contradict liberty and equality while sanctioning cruel punishments and holy war — is not moderate. Consequently, no one who advocates sharia can be a moderate, no matter how well-meaning he may be, no matter how heartfelt may be his conviction that this is God’s will, and no matter how much higher on the food chain he may be than Osama bin Laden.