Very thoughtful post. My personal take on it is unlike anything I've ever read anywhere. Up until the conversion of Constantine in around 300 AD, when the church became Rome's official religion, Christians were more or less a denomination of the Jewish religion, with Jews being sometimes in leadership roles. From Durant's work, I gather that there were Jewish-Christian congregations all over the Roman world.
But when Rome became officially Christian, I suspect that the schism (sp?) happened. Why? Here comes my own unique version of events: Because the Jews expected to be allowed back into Jerusalem, from which they had been banished in roughly 70AD after yet another rebellion against Rome. They must have raised hell over the issue, from within the church, and as a result the Romans tossed them out of the church. It may be that some of the gospels were very slightly edited to emphasize the split. Ever since, the Jews have been "out". Of course, Rome is pretty much out of it too, so the reasons for the split have long ago vanished. But these things have a momentum of their own.