The letter Punishing apostasy not arbitrary interpretation refers.
Abu Mubarak writes that since some major schools of Islam agree that apostasy is punishable by death, the subject is not debatable. As proof, he offers an excerpt from a book which says that this death punishment has been universally agreed upon by the 'ulama' and that it is based upon hadiths.
Unfortunately, this statement is the problem itself. With due respect, hadiths are by nature subjective. Various schools of Islamic thought will accept some hadiths and reject others. Hadiths have different potencies with some having markedly more authority than others.
The only point all Islamic scholars and laymen will agree upon without debate is the Holy Koran and from Abu Mubarak's letter, I can safely conclude that he cannot find any supporting text from the Holy Book itself to justify the death penalty for apostasy.
It is thus a great leap in assumption for him to say that the existing Islamic worldview is that apostasy is punishable by death. I respectfully suggest that he explore this subject thoroughly on the Internet.
He will find that there are a whole lot of highly respectable and devout Muslims in the world - scholars, clergy and laymen alike - who believe otherwise.