Initially, Jusaism was a culture and strictly a religion, never a race. That's why the term anti-Semitic makes no sense, as Arabs are also semitic. There was really no such thing as an atheistical Jew before the 16th century, other than what religious Jews classified as fraudulent Jews, or non-Jews.

During the 16th century, Jews were persecuted in the Iberian Peninsula. Many secretly converted to Christianity, others practiced their true religion in secret, whilst others too, disowned their religion attacking their own.

When the Jesuits created the Blood Libels Laws, and a large swath of Jews subsequently thought of Judaism as a biblically historical purity of the blood, both sides then fought among themselves.

The reformed Jews having disowned their religious ancestry latched unto to the supremacist blood purity ideology, which was a strict feature of Orthodox Jews during biblical times.

What we see today, are some Jews, very powerful, who believe Judaism as simply a race or purity of Blood. These same Jews having disowned the religious connotation of Judaism held onto the 'chosen one' ideologues and Holy land belief, that was merely a feature of religious Jews.

The Jew haters created the anti-Semitic canard to classify Judaism as a race in order to better categorize and persecute Jews.