Does the Messianic Jew give up his ethnicity, too?
Maybe I have it wrong. I don't know. But this is just how conservative blacks are treated by other blacks. Somehow, according to them at least, being a conservative erases "blackness." How does being Christian erase the ethnicity of being Jewish?
I have a hard time with that one.
As for "Jewish ethnicity" it is a vague enough term. I think people use that term as a "weak form" cultural signifier. In other words if you have no particular cultural identity other then "American" or "New Yorker", but you want to give someone a clue of where you fit in to the American Pageant, it can help them, even if you are an Atheist to say that, "my granparents were Lutheran farmers in Minnesota" or "my grandparents were Russian Jews." It tells people some clues about where you are coming from culturally. If I had to state the "ethnicity" of a Jew for Jesus whose grandparents were Russian Jews, I would say "He was born Jewish, but he joined a cult."
I have a hard time with that one.
You bring up a good point. Of course there are plenty of people who are ethnically (or "racially") and halachiclly (according to Torah law) Jewish because there was a Jewish woman somewhere down the female ancestral path. They might not even know it, but they are still Jews. But there is more to being Jewish than DNA. There is a religion called "Judaism" which "(racial) Jews for Jesus" do not practice or believe in.
If the "Jews for Jesus" could actually trace their ancestry in an unbroken progression all the way back to the days of Jesus himself, meticulous observing all the laws of Judaism and also Christianity, then they could legitimately claim to be a "Jewish sect." However, they are a gentile missionary society that targets the assimilated and the religiously illiterate. They have no schools or seminaries of their own, they get all their training from Christian evangelical institutions.