This is an interesting story:
So, who is a Jew?
And why do they need to live apart from other groups?
Yael converted to Judaism in 1992, and for the next 15 years she lived in Israel, celebrating the major holidays and teaching her children about the Jewish faith.
But when she and her husband sought a divorce last year, she said, the ultra-Orthodox rabbis in charge of the process had some questions. Among them: Did Yael observe the Sabbath? Did she obey the prohibition on sex during and after menstruation?
Dissatisfied with the answers, the rabbis nullified her conversion. Yael did not need a divorce, they ruled, because she had never been married. She had never been married because she had never been Jewish. And because she had never been Jewish, her children were not, either.
http://www.washingtonpost.com/wp-dyn/content/article/2008/08/29/AR2008082903594.html
So, who is a Jew?
On one side are ultra-Orthodox leaders who are using their long-standing dominance of Israel's rabbinical court system -- which has authority over marriages, divorces and conversions -- to tighten restrictions governing who can become Jewish. They see themselves as defending the religious purity of a people who, according to their interpretation of Jewish law, need to live apart from other groups.
And why do they need to live apart from other groups?