Intermarriage isn’t bad per se. Jews, including the patriarchs and Moses, intermarried. Edomites and probably Khaganate Turks were massively converted to Judaism. The Torah prohibits intermarriage only with enemy tribes (Deuteronomy 7:3) specifically because of their hostility and paganism. Marriage to Gentile women could not have been a problem. The marriage ceremony was religious, and so Gentile brides had to convert before marriage. They irreversibly joined the people of Israel after the marriage by living and suffering among Jews.

The situation with Jewish women marrying Gentiles is not clear. Even if the Jews refrained from participation in pagan rites besides marriages, their children—contrary to the rabbinical doctrine of maternal lineage—followed their father’s pagan religion. Jewish concubines, though slaves, could not be sold to other nations (Exodus 21:8); presumably, free women enjoyed no less protection.

The problem of intermarriage was apparent and the prohibition strengthened. Originally, Jews were only commanded not to take wives from hostile foreign tribes (Exodus 34:16); Deuteronomy 7:3 expands the otherwise identical prohibition to include marriage of Jewish girls to males of hostile tribes. After the Exile, the prohibition already covered matter-of-factly marriages with any foreigners (Ezra 10:11).

Joshua 23:12 condemns intermarriage with Canaanite aborigines for political reasons, and Judges 3:6 does so because intermarriage leads to paganism. 1Kings 11:2 confirms our understanding that the Torah prohibits intermarriage only with certain hostile nations: “of the nations concerning which…” The prohibition’s expansion follows the logic of the Torah. Jews should not marry the members of any hostile or staunchly pagan tribes. By the time the Jews returned from Babylon, all neighbors were hostile, hence Nehemiah laments intermarriage with residents of Ashdod who are not specifically mentioned in the prohibitive commandment. After two thousand years of Christianity, every white nation had developed built-in anti-Semitism. The biblical Canaanites are long gone, but Palestinian Arabs took their place as irreconcilable enemies of Jews. Every non-Jewish religion except Islam can be described as pagan. Theoretically, non-white atheists are neither pagans nor inherently hostile to the Jews, and are acceptable spouses if converted. Obviously, there are non-religious problems with black spouses; you don’t want your child to count on affirmative action to join a university.

Living with a spouse from your own people is more comfortable than living with a Jew-friendly foreigner.