Let's look into this.
Punishment by death for apostasy from Islam is firmly rooted in the most holy Muslim texts -- both the Koran (verses such as 2:217 and 4:89)
They ask thee about fighting in the sacred month. Say: fighting it is a grave (offense). And hindering from Allah's way and denying Him and the Sacred Mosque and turning its people out of it, are still graver with Allah; and persecution is graver with Allah; and persecution (fitna - persecution, trial, etc.) is graver than slaughter. And they will not cease fighting you until they turn you back from your religion, if they can. And whoever of you turns back from his religion, then he dies while an unbeliever -- these it is whose works go for nothing in this world and the Hereafter. And they are the companions of the Fire: therein they will abide. - 2:217
This ayah condemns those who attempt to proselytize Muslims and who prevent them from worshiping freely in the Masjid al-Haram. Moreover, it's made clear that the disbelievers being referenced are "fighting" Muslims with the intent of making them convert to another religion. Of those who abandon Islam, it is said that anything that they may accomplish is nullified in the sight of Allah (SWT) and that they'll receive their due punishment in the hereafter. No earthly punishment is prescribed, so the claim that this ayah provides justification for executing apostates is dishonest and inaccurate. The next ayah you cite proves my point rather than yours. Let's read it along with the ayah that immediately follows it:
They long that you should disbelieve as they have disbelieved so that you might be on the same level; so take not from among them friends until they flee in AllahÂ’s way. Then if they turn back, seize them and kill them wherever you find them, and take no friend nor helper from among them, except those who join a people between whom and you there is an alliance, or who come to you, their hearts shrinking from fighting you or fighting their own people. And if Allah had pleased, He would have given them power over you, so that they would have fought you. So if they withdraw from you and fight you not and offer you peace, then Allah allows you no way against them. - 4:89-90
The passage hardly requires an explanation. If the person in question "withdraws" from the Muslims (ie: becomes an apostate), attacking him is not permissible unless he takes up arms against Muslims.
Narrated Jabir: A bedouin came to the Prophet and said, "Please take my Pledge of allegiance for Islam." So the Prophet took from him the Pledge of allegiance for Islam. He came the next day with a fever and said to the Prophet "Cancel my pledge." But the Prophet refused and when the bedouin went away (from Madinah,) the Prophet said, "Madinah is like a pair of bellows: It expels its impurities and brightens and clears its good."
- Sahih Bukhari, Ahkaam ("Judgements"), no. 323.
The same hadith is reported in nos. 316 and 318 of that book as well as no. 107 of
Virtues of Madinah and no. 424 of
Holding Fast to the Quran and Sunnah.
More:
Is Apostasy a Capital Crime in Islam? - IslamOnline.net - Living Sharia'h
Sharia is derived from the Qur'an and Ahadith. Law with no firm basis in scripture is not Sharia.
See the link above.
This is untrue. The Shafi'i Grand Mufti, Ali Gomaa, does not believe that apostasy is a capital offense under Islam.
Ali Gomaa - Wikipedia, the free encyclopedia
Nope. Grand Ayatollah Hossein-Ali Montazeri disagrees.
Hosein-Ali Montazeri - Wikipedia, the free encyclopedia
The Middle Ages were a period of particularly high intolerance in Islam. A legal opinion issued during that period was not necessarily reflective of the actual teachings of the religion.
The contemporary (i.e., 1991) Al-Azhar (Cairo) Islamic Research Academy-endorsed Shafi'i manual of Islamic Law, 'Umdat al-Salik (pp. 595-96) states:
Reliance of the Traveler is not contemporary; it was written by Ahmad ibn Naqib al-Misri (d. 1367 CE.) You're referring to the 1990 translation of that work by Shaykh Nuh Ha Mim Keller. The Shafi'i position on apostasy was articulated by Grand Mufti Ali Gomaa; see above.
You'll forgive me for not addressing the rest of the post, as it deals with individuals whose opinions hold no real weight in Islam.
Wa 'alaykum as-salam.