This is not a question for quick lunch hour responses. That won’t stop me from giving one, though.
I really don’t know. But I have pondered it my whole life, always knowing my dad was almost murdered for being a tiny Jewish child in Hitler’s Germany.
Maybe a religious reason for hating Jews could be that Jews don’t worship or have the same reference for Jesus? Maybe for some that could shake their own Christian faith? And thus leave them with too much cognitive dissonance to accept or love these nonbelievers, so they start name calling?
Customs being different? All the Jewish people reading, so thus have social advantages over the mostly illiterate fellow peasants? Kings used to hire them to do all the reading etc.
Jews throughout the ages have been cohesive as a group, which can be very annoying, even through, often through, the worst calamities. They “never belonged” in any of the countries and the new kids are always picked on.
Maybe genetics: maybe matchmaking put parents together more carefully, plus the forced education of every boy, combining to increase the average IQ and thus make intelligence and streetwise/cleverness prized. The lawyers, doctors, moneyhandlers, etc might have engendered an appearance of unfair advantage over others?
Jews in many locations had to scramble for livelihoods. They couldn’t work in every field because of their laws, nor were they allowed in many professional guilds. And yet they succeeded financially often enough. Envy?
Because of the rules of the Torah, Jews were reluctant to assimilate into societies. They refused to eat foods given to other gods. They were reluctant to marry foreign women. In short, they stayed out on the fringe. Naturally, it was easy to make them the scapegoat. If you had a plague, it was probably the Jews. Crops failed? Jews. Economy tanked. Guess who, the Jew.
Because they didn’t really assimilate, it was hard to get political loyalty from them. They stood up for the underdog because they knew they were the next underdog. They didn’t as much oppose the government as refuse to walk in locked step.
Hitler used the most common tactic. He blamed them for everything that went wrong. It was easier for the Gentiles to go along with it than do any research and risk reprisals. Anti-Semitism is solely based on the person’s ignorance of the truth and willingness to believe any lie. When you are holding the proverbial hammer, every Jew is not a nail. Every nail is a Jew. It’s just that easy for them. Every bank president is a Jew because you can’t be a bank President unless you are Jew. That’s the way they think.