What is the difference between trying to a preserve a specific culture and xenophobia?

A friend of mine just got back from the Birthright Israel trip. He said that on the trip, participants were subtly encouraged to make sure they marry other Jews to keep the culture alive.

As a persecuted group I can certainly understand why the Jewish people have an impulse to preserve their culture. But I don’t see any difference between this and anti-miscegenation. Like, by definition, they’re the same thing. Isn’t refusing to marry someone outside of your own culture fundamentally xenophobic? And haven’t we, as a society, decided that xenophobia causes a lot of strife and suffering and produces nothing of value? Or is this “preservation of culture” argument a valid defense for xenophobia? Am I missing something here?