The American author Sherry Jones is either very brave or very foolhardy. She has written a novel about Mohammed, focusing on his relationship with his favourite wife, A'isha.
A professor of Muslim history, Denise Spellberg of the University of Texas, has described the book as "very ugly, stupid … soft-core pornography". Miss Jones can turn the other cheek.
The words of Anjem Choudhary, a one-time member of the extremist Islamist group al-Mujaharoun, are not so easy to brush aside.
Speaking after a firebomb attack on the home of the book's London publisher, he describes the novel as "an attack on the honour of Mohammed" and adds: "It is clearly stipulated in Muslim law that any kind of attack on his honour carries the death penalty."
Such an outrageous comment takes us back 20 years, to when Salman Rushdie was subjected to a fatwa by Ayatollah Khomeini, the supreme leader of Iran, on the grounds that he had committed blasphemy and apostasy in his book, The Satanic Verses. It is important to remember what then happened.
There were bomb attacks on bookshops in London, York and High Wycombe; the Japanese translator of the book was stabbed to death; the Italian translator was also stabbed, but survived; an arson attack against the book's Turkish translator resulted in the deaths of 37 people.
Mr Choudhary's words, therefore, should not be dismissed as just ugly rhetoric. They indicate that radical Islamist opinion remains dangerously rebarbative.
Isn't it time that moderate Muslims spoke out loud and long against the way a tiny minority of zealots can dominate the political debate and constantly depict Islam as intolerant and bigoted, when, in reality, those words apply only to its most extreme, blinkered adherents?