Shalom when I was in israel recently I was speaking to a friend of mine in shul about being Jewish, he was telling me how both his older brother and sister are in the process of marrying out, he understood how much it was hurting his parents but then questioned, "I understand that if I care about not only being Jewish but the continuity of the Jewish people as well then I must not marry out. However seeing as I’m not frum, I dont keep kosher or Shabbat I can’t see any reason why I need to limit myself by actively remaining Jewish i.e. marrying in and maintaining some sort of connection." My answer at the time was you must come to Israel, however this does not answer the deeper question of why should anyone who is not frum remain Jewish?
I'd like to answer with a question. Do you ask your self why do you want to live? Well the answer should be no, and that’s the right answer. Someone that needs a reason to live - is sick. It is suppose to be the most simple and natural feeling – to want to live. If one does ask you should answer but the question itself should be alarming. Same is with being Jewish and wanting your kids to be so. If you have to ask yourself why being Jewish that already means that something is wrong. The normal non observant Jew that eats non kosher and doesn’t keep Shabbat does not ask himself this question and that proves a normal and healthy Jewish identity. However if you need to ask you need to find the answer that suits you. First of all we believe that the Mitzvot of Torah apply to all Jews religious or not so the only real reason I can give you is that as Jews we are commanded not to marry out of the faith and Jews do what is right by Torah, especially with such fundamental issues. Secondly – that is your heritage, your past and your future, you can't just turn your back on your legacy and walk away – it's wrong morally and it will eventually cause you pain. You as an adult can't ignore your responsibilities for the sake of what deceptively looks like selfish pleasure. Thirdly – on a purely practical level – marrying out is almost like begging for marriage and child raising problems. Would you Bar Mitzvah your kids? What day school would they attend? They are likely to grow with identity crises. Can the spouse understand and tolerate your Jewish needs? When the romantic love fades out you need strong mutual basis to support the marriage. Many of those couples end up braking up the marriage, causing much pain to themselves and their children.