The same sort of Jew hatred that inspired accusations that Jews are Christ killers, that Jews kidnap Christian babies and use their blood to bake Matzah for Passover, etc... is the same sort of Jew hatred that inspired a Russian document known as the Protocols of the Elders of Zion, an account of a fictional meeting of Jewish leaders that "prove" the Jewish plot to take over the world.
While it is true that this document has been identified as nothing but a fraud and a forgery, written and disseminated for the purpose of stoking the flames of antisemitism, many Arab governments (including but not limited to those of Saudi Arabia, Egypt, Iraq, Libya, and Hamas) insist that the document is a genuine description of a real plot of the Jews to take over the world.
Meanwhile, people who so blindly and virulently hate the Jews often mask their hatred as being hatred not of Jews, but of "Zionists". They insist "accusations of antisemitism are empty because they don't understand the difference between criticisms of the Israeli government and statements against Jews."
Problem is, the people who are busy hating Jews and/or Israelis very rarely make a distinction... and in many cases, from their point of view, there is no distinction.
When they think of Zionism, they think "protocols of the elders of Zion", so they very much misunderstand what Zionism really is, and stand by their hatred of it.
What it boils down to is, antisemitism and anti Zionism are one in the same... except in modern times it's not so fashionable to admit to hating Jews, so to appeal to the rest of the world, they call it a hatred of the policies of the government of Israel.
And since Israel has refused to roll over and die, and they have a sovereign state, and a strong military, and an excellent economy, and the Palestinians have none of those things, the Palestinians have the sympathy of the western world because they're seen as the underdog next to a big, bad, brutal Israel who just wants to grab land and deny Palestinians their self determination.
It's all a load of crap, but that's the way a lot of people see it. And so when they figure all they're doing is criticizing Israeli government policies, they have no idea that they're really feeding into the antisemitic propaganda of a people who hate Jews and wish for the rest of the world to do the same.
