There is, in fact, a compelling anthropological reason for the isolation and demonization of Jews in Europe (in particular).
It’s a phenom that is by no means restricted to Jews. What is necesary is to have a reasonably rigidly stratified society, with a small upper class ruling a much larger traditional peasantry; and a small group of (tolerated) outsiders to the system. These people, having no local ties, fill the role of functionaries to the upper class - often undertaking unpopular jobs such as “moneylender” or “rent collecter” (Jews often did this job in, for example, Ukraine for Polish overlords). In short, to fill out a sort of middle class.
In traditional society, the upper class cannot do these tasks without losing caste, and the peasantry generally cannot because it would alienate them from existing communal ties, or lead to excessive ‘corruption’ of the letting-the-brother-in-law-off-the-rent-hook kind. A “tolerated” outsider group fills the gap; in the case of Jews, they were “tolerated” by official Christian doctrine but not considered part of society; their ties were to each other, not to the mass of pesantry; the upper class protected them from the wrath of the peasants, while “milking” them (thus not arousing anger against itself). In England, for example, Jews were considered officially the ‘property’ of the English Crown which set up a special “Exchequer of the Jews” and thus profited from money-lending without appearing to do any itself.
The system breaks down when an indgenous non-minority middle class springs up. The “tolerated” group is no longer necessary and so is soon discarded (that is, official protection is withdrawn). In Western Europe, for example, the Jews lost their monopoly on banking activities to such groups as the Templars and then the Italian banking families - no longer needed, the monarchs which once protected them sometimes decided to make one last profit by expropriating all their money and expelling them (as I believe Edward I of England did).
Point is, that similar groups have a similar social niche - for example, the “Overseas Chinese” in Indonesia.
To answer the question - Jews became officially wholly “evil” in Europe (as opposed to “tolerated”) when, as a class, they were considered no longer really necessary by the upper class. In the case of England, this has a more or less exact date: 1290.