I have often heard that religious and traditional Jews are very concerned with intermarriage with non-Jews and strongly discourage it. But halachically, what is the support for the prohibition?
I am assuming here that the marriage performed would be a civil one or a Christian marriage or something like that.
I know that intermarriage with the seven nations is prohibited in Torah, as well as a few others, like Moabites. But even rabbis now say that the descendants of those nations are so diluted that we cannot really determine that anymore.
The following article attempts to address this question, and admits that the rabbis typically base their prohibition on the prohibition from Torah about Caananite nations:
But it does not seem to make a clear case that ALL non Jews are forbidden. Also, today the danger of avodah zarah is not as it was before - today most Westerners are either monotheists following one of the Abrahamic religions, or some variety of skeptic or apathetic. So, I would like to know the major source for the prohibition of intermarriage today, and what this source says about the consequences of such an intermarriage.
In fact, even the halachic question of who is a Jew seems to be based on rabbis parsing a verse in a strange way to say it goes by the mother. A literal reading of TaNaKh may suggest it actually goes by the father. So, what does it even mean to marry a Jew or non-Jew when the person isn't fully observant?
In your answer, if you could also address Deuteronomy 21 which describes marrying women captured in battle, that would help clarify the matter as well, since any halachic interpretation should probably address Torah commandments that would seem to be problematic for the interpretation.