Why marry Jewish?

I got into a conversation with my friend the other day about marrying Jewish and conversion...I have always been brought up with the subtle suggestion by my grandparents my parents that marrying Jewish was a good idea; it ensures the survival of the Jewish people and is a source of common ground in a relationship. They also preached that conversion was a totally viable option. But really, if Judaism to me is a set of values and traditions, why is intermarriage such a big deal? If a couple decides to live a moral life, why do I care if they share the label of "Jew"? I'd rather the basic principles of the Torah and the moral values it teaches (respect and love for all things, resistance to oppression, charity) reach out to the rest of the world than continue a direct line of pure-blood Judaism. That is, I don't care what you label yourself (Christian, Jewish, Atheist etc) or if the labels disappear entirely in the end as long as you are living a moral life...Opinions?