There is at the center of all conspiracy theories a black hole waiting to devour all adherents to the satellites that revolve around it. Whether the conspiracy theory concerns UFO's, The Kennedy Assasination, 9/11 conspiracies, or various economic and social theories, sooner or later the True Believer ends up being pulled towards the Grand Unified Conspiracy Theory of Everything. Eventually, it all comes down to the Jews. Start with any part of the lunatic fringe, and stick with it long enough, and you will one day wake up in bed with Hitler.
This may be the result of conspiracism, the conviction that the social and political sphere has been infected by a foreign agency which, if expelled, will correct the imbalance and solve all of our problems. The inevitable question then, is, who is this enemy who has caused all the trouble? The answer is that there is no enemy.
Part of the disfunction of any society is due to pure self-interest without proper mechanisms of correction, a state of affairs which exists to some extent in all societies, but is far less prevalent in democracies than in corrupt totalitarian regimes. This results in a deficit of faith--not faith in a particular creed or creeds, but a loss of confidence that honest effort will be rewarded, forcing upon all the conclusion that the only way to beat the thieves is to join them.
But even in the best of societies, political, social, and economic arrangements will typically lag behind the demands of the current situation. This is unavoidable, due to the fact that overly progressive modifications to these arrangements can cause as much or more harm as benefit, leading to a reactionary backlash feared by responsible citizens of both conservative and progressive leanings. Indeed, traditional and neo-conservatives distrust progressives, not because they despise progress, but precisely because bold leaps forward can lead to reactionary leaps backward, erasing not only the gains of the current program but solid gains previously achieved. Both progressives and conservatives value progress, but conservatives emphasize caution, while progressive emphasize adaptation.
But this answer requires subtlety, and conspiracists don't have much use for subtlety. They are the very reactionary camp that conservatives fear. Conspiracists are nearly always disenfranchised, and for good reason. The very lack of intelligence, discipline, education, reasoning skills, or personal responsibility which throws them on hard times also makes them prone to believing in conspiracy theories. Their failures cannot be their fault, so someone must be holding them back. And so, they go looking for someone to blame. Still, even for the dedicated conspiracist, economic, political, and social arrangements are so mercurial that it is hard to point to one consistently coherent faction which could draw all of the various conspiracies together into a tidy bundle.
Enter the Jews. The Jews have been around for millenia, and there is a wide variety of anti-semitic material pumped out through the centuries to draw upon, authored by or at the behest of governments, demogogues, rival religions, and fellow conspiracists. Yet, what makes the Jews so attractive as a target is not just the mere fact of their survival, but their success against all odds. The Ashkenazy Jews of Europe are the product of the most intensive cultural selection regime in human history. As dissenters from the dominant religions in every place they have lived for the past two-thousand years, they have never enjoyed a safe haven where they could be certain to avoid persecution. Denied, for the most part, the right to own property, to join guilds, to hold titles or engage in politics, and even suffering exemption from the moral code which protected others of the dominant religion, the Ashkenazy Jews have lived under the threat of attack, loss of property, and sudden expulsion for most of European history.
If you are faced with the possibility of having to pick up and move quickly, security lies in portable wealth, which not only allows you to carry most of your fortune on your person, but to exchange this wealth in return for safe passage. Thus, the Jews came to value gold and jewelry, for the same reason that "diamonds are a girl's best friend." Women, too, were a powerless faction in society--if your husband owned all land, goods, and titles, the best you could hope for, in the event that everything went bad and a quick escape was required, was to take what you could carry. Jewelry is the ultimate mad money. But even jewelry wasn't a sure thing--you could be stopped and stripped by a gang of thieves, who could take everything you had. And after all, they were just Jews. The local constable might even be in on the deal.
Sheer selective pressure led the Jews to discover the one kind of wealth that could not be stolen by thieves: knowledge. You could lose your books, but not what you had learned from them. Knowledge, and the ability to use that knowledge, was the magic formula, and not just for the Jews, but for anyone in human society. And the Ashkenazy Jews had to be a little smarter and a little more adaptive than anyone else, just to land on their feet. As the centuries went by, the advantage that knowledge conferred grew. Jews survived in the worst of times, but flourished in the best of times.
To conspiracists, who seem to cherish ignorance as much as the Ashkenazy Jews valued knowledge, this ability to thrive in adversity must seem almost occult. The conspiracist cannot see how the Jews could do this without cheating, precisely because it is an ability the conspiracist lacks. There must be some cabal, some secret brotherhood, some dark, nefarious means by which the Jews are able to recover and rise to prominence. The myth of the Jewish banking conspiracy had its roots in the fact that the Jews did horde gold, and were not restricted by religion from loaning money with interest. Still, once European Christians figured out there was serious money to be made, they went into banking on a scale the Jews could scarcely dream of. The Rothschildes were successful bankers, but did not control the major banks. And it did not help that constant privation drove many Jews into the underworld--Fagin was not a typical Jew, but his type did exist. But these were exceptions rather than the rule.
Something which may play into the myth of Jewish malevolence is a trait that Jews share with scientists, and with any culture which is in its ascendancy: the bold and almost rapacious collection of knowledge. Americans and the Japanese tend to have the same trait, as the British and Romans did at the height of their Empires. In the terms of the politically correct, they lack "sensitivity". They ask blunt questions, tread casually on sacred ground, and will tear into the heart of another culture, taking what they can use and discarding the rest. To the ears of those who hold that culture sacred, these questions sound profane and offensive. Yet this very tendency is the mark of a vibrant civilization, which is not afraid to assimilate ideas from the outside. When a culture closes in on itself and fends off outside influences, its days of glory are past. It is no longer strong enough to fend for itself in the free market of ideas. To take offence at hard questions is a sure sign that one has stopped asking such questions oneself, the beginning of stagnation and death.
In fact, direct questions are a form of engagement and respect. Postmodern sensitivity is the product of a patronizing conviction that one's own culture is so overwhelming that it would crush all others. This is the attitude of an adult asking a child about Santa Claus, and underlying it is the certainty that the other person really has nothing to teach you--or at least, nothing that they can put into words. But most of all, it is the identification of opinion with ego, the idea that there are no beliefs that have a basis in fact. Postmodernists don't dig for the truth because they don't believe that there is any truth to find. The Ashkenazy Jews could not afford the luxury of relativism; success, and survival, are dependent on a clear picture of reality. An argument is about establishing the truth. It's not about you.
This is something which conspiracists, who are willing to entertain almost any scientific theory except the one supported by evidence, cannot seem to grasp. This is probably why conspiracists will immediately resort of ad hominem attacks when challenged. There is no truth, only authority; if you challenge my opinion, you are challenging me. To someone whose confidence in a theory is inversely proportional to the evidence supporting it, and who sees all contrary evidence as propaganda that proves the conspiracy, there is simply no other way to argue a point. And so, the more evidence that accumulates against the existence of the Vast Jewish Conspiracy, the stronger their belief in it becomes.