Many German Jews were very patriotic during World War 1. Quite a few fought and died for their country and its lousy cause. The problem was that the war was a lousy cause, like the Vietnam War and just about every war we ever fought after the Great War.
Germany started losing, and a dissident peace movement similar to the antiwar movement in the Vietnam era sprung up in Germany. Some of these people, but many others were just good Germans sink of junkers, kaisers and disgusting mess that was incipient German imperialism and militarism. The antiwar movement helped end the war, which was a good thing. After the war, which ended in Germany’s defeat, this protest movement began challenging many of the traditional views of the land which had dragged the nation into a stupid militaristic adventure that led to the massacre of a generation of European men. Many liberals, media people, comedians, musicians, show business types, politicians and intellectuals joined this movement.
Of course some were Jews but most were not. Keep in mind that Jews were maybe 1-2% of Germany at this point. The point here is that these Jews were not traitors at all any more than the rest of the liberals were. They were calling for a Cultural Revolution in Germany and challenging the reactionary views that led the nation to war.
This was the “stab in the back” that Hitler referred to. There was no stab in the back anymore than that the Vietnam War Protest Movement was a stab in the back. Hitler and the Free Officers were reactionary militarists. They were not OK people. They were like McNamara and LBJ on steroids. They were a bunch of lousy killers, militarists fighting for a no good cause. And really the entire liberal intelligentsia stabbed the country in the back, if anyone did.
But the stab in the back more than anything was self inflicted. Germany was losing a lousy war they started for no good reason. The Army and the militaristic state was stabbing its own self in the back in a form of perverse hari kari.