As someone who's half Jewish, I've long thought that the people who best understand Jewishness are other half Jews. More (much more) than religious identity, Jewishness connotes tribal identity -- true tribal identity. I can't think of a "religion" less welcoming of converts than Judaism. Jews don't prostelitize. They actively discourage conversion (it's an official part of the conversion process -- the sincere effort to discourage conversion). Once converted, the new Jew is never, truly, 100% accepted. Intermarriage is anathema. Half Jews simply don't feel the same tribal blood bond which exists in the minds of full Jews. Jews rightly fear intermarriage as being the greatest threat to the perpetuation of the tribe. It's a very emotional thing -- the tribal identity.
Anti-Semitism is based on more than the unfortunate concept of "Christ killing" as being the responsibility of the entire Jewish tribe, as opposed to the action of a few individuals in positions of power, who, like most such people, react harshly to perceived threats to that power (and I find that there is much in Catholic liturgy and priestly homilies which continues to perpetuate the "Christ killing" broad brush of tar -- a topic for another time).
A recurrent source of anti-Semitism is the disproportionate success, wealth, and economic power of Jewish people. It's a natural human reaction to be very resentful of these attributes in a closed and insular group of people. One of my favorite expressions relating to science is that "any experiment which has failed a thousand times should be viewed with suspicion." The idea that Jews can exist as a closed, insular tribe and continue to enjoy success, wealth, and power without generating a lot of resentment and suspicion is a hypothesis which as repeated failed, thoughout many centuries.
- Larry Weisenthal/Huntington Beach CA