I have to disagree that antisemitism is simply "anti-capitalism". If that were the case, why are the biggest Jew-haters also huge apologists for capitalism? These people hate us because they envy the success of the rich Jews in the existing system; rather than desiring the end of capitalism as a whole, they merely want to take the place of the "rich Jews" and live as the big capitalists themselves.
No, you're exactly right, but that's what Postone is getting at, I think. Note he says that anti-Semitism is a fetishized form of anti-capitalism. Capitalism meets a crisis, and instead of challenging the abstract domination of capitalism, which anti-Semites don't understand, they blame the Jews as stand-ins for it.
Capitalism's power is "abstract" because it naturalizes and objectifies the social relations between things (which are really the material relations between people) in the form of commodities, right? I don't really understand all of this, but Postone is arguing that Jews in the anti-Semitic mind take the form of a commodity.
The quality of abstractness, characteristic not only of the value dimension in its immediacy, but also, mediately, of the bourgeois state and law, became closely identified with the Jews. In a period when the concrete became glorified against the abstract, against “capitalism” and the bourgeois state, this became a fatal association. The Jews were rootless, international, and abstract. Modern anti-Semitism, then, is a particularly pernicious fetish form. Its power and danger result from its comprehensive worldview which explains and gives form to certain modes of anticapitalist discontent in a manner that leaves capitalism intact, by attacking the personifications of that social form.
A capitalist factory is a place where value is produced, which “unfortunately” has to take the form of the production of goods, of use-values. The concrete is produced as the necessary carrier of the abstract. The extermination camps were not a terrible version of such a factory but, rather, should be seen as its grotesque, Aryan, “anticapitalist” negation. Auschwitz was a factory to “destroy value,” that is, to destroy the personifications of the abstract. Its organization was that of a fiendish industrial process, the aim of which was to “liberate” the concrete from the abstract. The first step was to dehumanize, that is, to rip away the “mask” of humanity, of qualitative specificity, and reveal the Jews for what “they really are”—shadows, ciphers, numbered abstractions. The second step was to then eradicate that abstractness, to transform it into smoke, trying in the process to wrest away the last remnants of the concrete material “use-value”: clothes, gold, hair, soap.