Boteach (who is far more popular among Christians than Jews) defends his book this way:
http://www.gefenpublishinginisrael.com/2012/01/19/what-is-motivating-the-global-ban-on-kosher-jesus/
...Kosher Jesus goes back to the original gospel source materials to uncover the real story of Jesus and portray him for whom he was prior to later Christian editors significantly modifying the story to accommodate the Romans.
Jesus was, as many have argued before me, a Torah-observant Jew whose mission it was to restore Jewish observance fully among his Jewish brethren and fight Roman persecution. For doing so he was turned over by the Roman collaborator, High Priest Caiaphas, who owed his office to the Romans, and was murdered by the Roman prefect Pontias Pilate – the Saddam Hussein of the ancient world – for doing so.
Jesus was a martyr for his people who never claimed to be divine, who never changed the Torah, and who would be scandalized to see his teachings – nearly all of which I trace back to their earlier Jewish sources – misused to persecute his people.
It was Paul, who never met Jesus, who later deified him and said he came to get rid of Torah practice. But Jesus himself said the opposite, in Matthew 5:18, that anyone who does not keep the whole Torah would be cast out of heaven...
Who are the many who have argued before you? JC seemingly tries to nullify (G-d forbid) the Torah. And that is from Christian sources....the Jewish ones are quite sharp in their descriptions of him.