Answer:
   
   Children of intermarriages are statistically less likely to identify
   with Judaism than children raised by Jewish parents, so intermarriage
   weakens the Jewish people. Therefore, Jews across the spectrum oppose
   intermarriage in order to prevent this weakening.
   
   A large part of Jewish observance and identity centers on the home,
   family, and community. Religion is a part of daily life, in areas as
   diverse as making a blessing before wearing new clothes for the first
   time to thanking G-d before and after meals. Special occasions such as
   Shabbat and holidays carry special customs and observances. A home
   made by a Jew and a non-Jew is much less likely to be a "Jewish home".
   Where children are involved, they are most likely to grow up with a
   positive Jewish identity when they see both parents Jewishly
   connected.
   
   Also, for many people, a difference in religion is an added stress on
   a relationship. For this reason, many Jewish parents discourage
   intermarriage in their children in an honest attempt to help their
   children find long-term happiness.
   
   Given all this, what should be our attitude when intermarriage occurs?
   There are some that believe the intermarried couple should be
   ostracized. Others take a different view.
   
   First, if there are no children involved (as sometimes happens with
   elderly couple), then there is no real loss to the community in terms
   of future generations. If there is no conversion, each partner just
   practices their own religion.
   
   If there are children, or potential children, involved, the issue is
   different. Ostracizing the couple may have the side effect of
   destroying any positive attitudes towards Judaism, ensuring the
   children will not be Jewish. Remaining open to the couple, inviting
   them to family ceremonies, and showing them the beauty of Judaism can
   help educate the non-Jewish partner. Even if the partner doesn't want
   to convert, it may convince the partner to raise the children Jewish,
   and (if appropriate) have the children be formally converted into
   Judaism. Often, having children will make a parent want to reconnect
   with their spiritual heritage. The Jewish parent may feel an increase
   desire towards reconnecting with Judaism, and keeping their children
   connected. This desired would be destroyed if the couple had been
   ostracized.
   
   The best thing to do is to keep an open mind. Believe that the couple
   is not lost. By demonstrating to them the joy and beauty of Judaism,
   they may choose to return or increase their Jewish practices.