[rdb3]

It is a matter of Jewish Law. A Jew that makes a public declaration to attach himslef to another G-d is considered an apostate.

Okay, fine. But I'm not speaking in the religious sense. I'm talking specifically about ethnicity. How does becoming a Christian change that?

[Nachum]

Okay, fine. But I'm not speaking in the religious sense. I'm talking specifically about ethnicity. How does becoming a Christian change that?

One is not merely a Jew by merit of their birth, but also by a minimal standard of behavior. This standard even applies among secular Jews. When a Jew becomes a Christian, it is a very personal attack on Jewish identity. One cannot be both, as much as some Christians try to sell the idea.