I wouldn't say Islam is retarded. It's just a historical event like any other. More precisely, the final and logical consequence of a syphilitic cameller's spiral criminal career in the 7th-century Arabian Peninsula: once you start holding up caravans, you can end up founding a religion.
To write a delirious story about the hippie son of a Jewish carpenter is not that uncommon, actually. I've read worse things.
That what I don't understand is why people take those things seriously.