Rabbinical Schools Bar Students in Taboo Relationships

I just read in the Jewish Advocate weekly newspaper that entry to rabbinical school in all branches of Judaism is barred to people who are married or in a committed relationship to non-Jews. This is despite the fact that intermarried families are now welcome to join, as lay members, all Jewish congregations but the Orthodox. It is also despite the fact that the Reformed and Reconstructionist branches recognize children with Jewish fathers but non-Jewish mothers as Jews, going against centuries of tradition. The reason given for barring entry to rabbinical school, even in the latter two branches of Judaism, to those in hetero-religious relationships is "the importance of family modelling."
It seems to me that Judaism is on a self-destructive path. A recent survey of Americans has determined that a very large percentage have changed religions, although many of the switchers have jumped from one Protestant denomination to another. Catholicism has lost many non-Hispanic whites to Protestantism, but Latin-American immigrants have filled the deficit. Given the large degree of religious fluidity in the U.S., a religion that only worries about people leaving but does nothing to welcome newcomers, or even deters potential converts, will inevitably shrink in numbers. It's like trying to plug a large leak in a swimming pool with chewing gum while closing the intake valve to allow no more that a drip to come in. If Judaism is to survive and thrive, this attitude has to change. Conversion to Judaism should be based on sincerity of motivation and belief and little else.
The basis for matrilineal descent and difficulty of conversion appears to lie in the notion that the Jewish People are a race rather than a religion. This is basically hogwash because a large percentage of Jews cannot be physically distinguished from non-Jews. Too much interbreeding within a group leads to genetic problems as evidence by Tay-Sachs disease that befalls only those of Jewish descent. I say, let Judaism welcome all who have a sincere interest in joining the religion. Let Judaism be a true religion, not a race, and do not try to fight the religious fluidity that characterizes a free society. Yes, Judaism will lose some adherents, but will also gain some. And by being more welcoming, it is likely that Judaism will expand in numbers and regain its vitality.