... it has been observed by many others that Josephus' names for James and Jesus are quite unusual for a Christian. By the time of Hegesippus, Christians typically called James "the Just." Even as early as the 50s AD Paul, who was personally acquainted with James, calls him and Jesus' other brothers "brothers of the Lord" (Gal 1:19; 1 Cor 9:5). Moreover, the expression "Jesus called the Christ (Ant.20.200), although not derogatory, certainly implies some distance from the Christian affirmation that Jesus is the Christ.
... [also note] the implausibility of a second or third century Christian at all forging a passage about one of Jesus' brothers. Yet already by the mid to late second century, the mere fact that Jesus had brothers or even half brothers was becoming highly problematic in Christian circles. The Protevangelium of James and the Gospel of Peter were written in this period, and both of these Biblical apocrypha make Jesus' brothers into step-brothers because they are concerned to maintain the idea that Mary was a perpetual virgin, without contradicting Luke 2:7 that Jesus was her first-born son. Although the Protevangelium was never canonized, its influence on Christian understanding about Jesus family even in this period was enormous. Origen, who clearly did not consider it scripture, approved of its ideas about Mary's perpetual virginity. ... [and] Origen evidently found it difficult to believe that Jesus had a biological half-brother: when citing Josephus' passage on James in his public apology Contra Celsum, he hastens to assure even its mainly non-Christian target audience that Paul described "him as the Lord's brother, not referring so much to their blood relationship or common upbringing as to morality and understanding." By the late fourth century, even the idea that Jesus' brothers are no more than half-brothers was beginning to border on heresy in the West, as we learn from Jerome's Adversus Helvidium, in which Jerome insisted that Jesus' New Testament are actually maternal cousins. Jerome's idea that the brothers mentioned in the New Testament are actually Jesus' cousins was not challenged in the Western church even during the Reformation. Only in the last two centuries has it become commonplace for Protestants to affirm that they must be at least half-brothers. Given the reluctance of many Christans to affirm openly that Jesus had brothers or half-brothers even as early as the middle tp late second century, the idea that Josephus' passage about "James the brother of Jesus called the Christ" was composed by some ancient Christian can be safely laid to rest.
opcorn: