Why do people refuse to believe Jesus is Jewish?

Even Robbin Williams speaks of the obvious fact that Jesus was Jewish. Why is it that there are still people out there, both Christian and non-Christian, who refuse to believe that he was Jewish? I'm surprised when  Christians who have attended church for most of their life, heard sermons preached from the Bible, learned biblical stories about Jesus in church and from family, grow up, get married in church and pronounced married with a blessing prayed to Jesus, do not realize that he was Jewish?

• Why do you think this is?
• Why is there are mental block in followers of Jesus about his being Jewish yet Robbin Williams believes it wholeheartedly?
• Why is there such blind spot in our Christian culture about Jesus being Jewish?
• How would you break the news to them?

Christianity vs. Jesus the Messiah?

This Jewish convert spoke of the hindrance to Jesus created by Christianity throughout history.  Coming to realize that Jesus is the Messiah and accepting him as Lord and Saviour, he now deals with a family that is confused about why he has converted to  a faith that was the source of much strife for the Jewish people throughout history.

• What would be the equivalent for a Christian family experiencing a child accepting a faith that has hurt Christians throughout history?
• How difficult is it for Jews to accept Jesus as Messiah?
• How can we speak of Jesus in a way that will cause Jews to consider him as Messiah?
• How can we speak of Jesus in a way that conveys his Divinity without being offense to Jews?
• Why does Jesus appear in world history as a Jew?
• Could God have simply done this another way .i.e., Jesus having come attached to another people group?