The situation in Arabia that is addressed by the Quran is most likely not as straight forward as in your last E Mail.
a) Firstly the fact is, despite 9.30, that if the Nashara were the Nazarenes, they were of Hebrew origin and "the guardians of pure monotheism / Tauhid", in contrast to Greek influenced Gentile Christianity. The problem is that ben elohim (son of God) was a perfectly acceptable term in their language as far as Tauhid is concerned, and was used by the Messengers of God all the way back to Nabi Musa. It was purely a figure of speech. This is rarely understood by Muslims. "Hebrew figures of speech make great use of sonship terminology, e.g., sons of Babylon, sons of the kingdom, sons of the evil one, sons of thunder, sons of peace, sons of the light, sons of darkness, sons of heaven, and sons of the resurrection. Obviously, such titles neither imply biological offspring, nor suggest that a woman could literally be impregnated by thunder or light."
b) The problem occurs when the Nazarenes / Nashara use that phrase in Arabia. "Obviously, literal translation of ben elohim (son of God) was even more vulnerable to evolve into heresy in Arabia not only because of the more restrictive use of terms like ibn and walad, but also because of how easily such titles were confused by pagan idolaters to refer to that which the Qur’a¯n condemns unequivocally." . This is rarely appreciated within Islam. Son of God is a linguistic problem between Hebrew and Arabic.
c) As mentioned previously, Arabia was known for heresies prior to Muhammad. Possibly because of the linguistic issue, also surely that there was no Torah / Injil in their language.... which the Quran refers to people trying to sell fragments. It was a complex problem....