In the present ecumenical climate, in which, thankfully, Jews and Christians are working to overcome their long hostility, there is a tendency among Christian and Jewish scholars alike to maximize the connection between the two faiths (something amenable to the Christian apologetical agenda, since this trend minimizes possible influences on early Christianity from Hellenistic Mystery Religions or Gnosticism). An important part of this interfaith program is to make Jesus as conventional a Jew as possible. In my opinion, such a move is more of a construction of Christology than a sketch of the historical Jesus. That is, it is an attempt to come up with a Christian "Jesus Christ" that will prove more useful for ecumenical dialogue. The a priori character of the whole endeavor is evident from the way such scholars simply assume that the gospel stories and sayings must be interpreted in Jewish categories even when there are as good or better paradigms available to make sense of the sayings, for example, Cynic or Gnostic. As long as there is a Jewish parallel available, even when forced, these scholars will automatically prefer it. This is theological reasoning, not historical criticism (Price, p. 247, italics mine).
My favorite biblical scholar and atheist, Robert Price here does an excellent job exposing what is at the heart of the "Jewish roots" of Jesus movement—an attempt at ecumenism (commendable as that may be) and a veiled attempt to set forth "Jewish roots" as the way to reveal the historical Jesus. As Price points out, there are often better Cynic, Gnostic, or Mystery Religion parallels to the platitudes and the actions of Jesus in the gospels than the Jewish ones a priori esteemed to the exclusion of all others. As healthy as the ecumenism between Christianity and Judaism has been, a peace has been forged at the expense of serious Jesus scholarship among those unwilling to consider that Jesus is a recapitulation of the dying-rising man-gods of ancient lore.
Price, Robert. The Incredible Shrinking Son of Man. Prometheus Books, New York: 2003.