The closeness of Christians to Jews in the early centuries of the Common Era was troubling to the nascent Church Fathers. They repeatedly speak out against it because they understood that many Christians saw Jews in a very different light than what the emerging church was promoting.
This closeness also bothers many people today, particularly in the Jewish community for understandable reasons. Assimiliation through intermarriage or through an abandonment of Jewish identity through Americanization is a very real concern. The animus of previous centuries, however is markedly different.
Check out Complex Identities: Too Close for Comfort.