I've read all the theories: jealousy of Jewish wealth (there've been many poor Jews and they've been just as despised), envy of Jewish "smarts" (then why isn't there an equally universal hatred of Asians? and there are plenty of not-so-intelligent Jews), psychiatric aberration (if only--then it'd be much less prevalent), political stance (we've been blamed for both capitalism and communism), Zionism (plenty of Jew-hatred before Herzl and the State of Israel), and finally resentment of Jewish ethical monotheism (I don't think that's what goes through the average anti-Semite's head---"I hate the belief in one God with moral expectations, so I'm gonna take it out on its inventors"--no one thinks like that).

No, I've come to the conclusion that anti-Semitism exists because...it exists. It's a self-perpetuating meme. Those who hate Jews do so because they were taught to do so by other people who hated Jews, and so on. The fact that we're arguably the oldest continuous civilization still around may account for the persistence of Jew-hatred throughout history. If the Sumerians were still with us, I'd bet people would ask, "Why is there anti-Sumerianism?"