I disagree. Judaism is not an ethnic group, it's many absolutely different and disjunct ethnic groups, that only have religion in common. A Jew from Yemen has nothing else in common with a Jew from Poland. Different language, different food,. different music, different physical resemblance, different interpretation of the Torah, etc.

I recommend reading The Invention of the Jewish People, by Shlomo Sand.

As a practical example. When my father (Ashkenazi) married my mother (Sephardic), my father's grandma was devastated, because he was marrying a non-jew.