They are only an economic threat...
I see antisemitism coming in several flavors, according to motivation:
- Pure stupidity, i.e. the belief that Jews cook Christian children into meatloafs and the like. Believe it or not this is what was behind the last couple of big Russian pogroms including Kishenyev.
- Rotschildes, Soros, Bank of England, legalization of fractional-reserve banking etc. These people have brought about gigantic harm in the world. Granted ordinary Jews neither know anything about nor give a rat's ass about banking, they suffer from the ill will this stuff generates.
- Communism, addiction to left-wing causes. I would guess that pretty much everybody in Europe by the late 1930s knew somebody who had died in Stalin's artificial famines in the Ukraine. Again the typical Jew neither knew anything about nor gave a rat's ass about communism, but the original bolsheviks were mostly Jews and the ordinary Jew gets blamed for it.
- Ghettos. Ghetto dwellers in America today are generally despised by ordinary middle-class people. I'd assume the same was true in Europe in the early 1900s.
- Islam. Islam deliberately and directly promulgates hatred of Jews today. In the middle ages there was likely a question of Jews seeming to be doing too well for themselves under muslim rule in places like Spain while Christians suffered and were oppressed. Jews participating in even one crusade would have cured that one. There is probably another crusade coming up shortly, Jews should make certain they do not get left out...
I might have missed something or left something out but that's what I'd view as most of it. Claiming that antisemitism can be explained in simple economic terms strikes me as misguided.
In my opinion, you left out the "brand" of alienation from Jews in the large urban centers (in the U.S.). This might be based on the belief that "chosen to receive the Ten Commandments" really means that Jews think that they are "superior," based on either a theological concept of being "chosen by God," or superior in intellect (chosen to go to college?).
It is my belief that since the Jewish culture emphasizes education many Jews manage to overcome any childhood difficulties in school, and get an education beyond high school. In effect, they seem to cluster, in my opinion, in the middle of the great human bellcurve. So, if we think of Jews having a greater percentage to being of average intelligence (like many a middle American), then that left-half of the bellcurve might think of Jews as "acting" smart/superior, since it is part of the "Gentile culture" to think that Jews have no right to be equals to any Gentile worth his/her Christmas stocking, so to speak.
In effect, anti-Semitism might just be today the indelible results of a two-thousand year learning curve by Christianity and a lesser timed learning curve by Islam. In other words, both Christianity and Islam, in their repective worlds, made themselves on top of the pecking order, and Jews living as minorities in both worlds were a priori not to be treated as equals. America is an affront to this thinking for many, in that Jews are quite equal, and I do believe it rankles many a Gentile to think that this should be so. Especially, if one's grandparents came from a land where Jews acted deferent to a Christian. Old thinking is hard to change, in my opinion.
All this makes sense when one remembers (if one had prior lives) that the pagans just thought of Jews as those laughable odd fellows that believed in one god. So, it took Christianity to come up with a better reason to not think of Jews as equals. And, since that lesson was taught for almost two millenia, it is hard to erase. However, it all stems from Jews being a minority that just seemed different than other minorities, in that they maintained that they were in no rush to assimilate into the majority, and oddly not even out populate the majority. And, the masses being just the masses did not always give Jews the incentive to assimilate into their culture. Just my opinion, naturally.