In its way, this sort of wised up, snarky tone which American leftists evince toward other American leftists is its own defeat. After all, no one copping such a rebarbative attitude is likely to convince many people, keep many friends, or leave many bridges un-burned. The very weariness of the tone is a register of defeat, in fact.
There may be a history of cultism in the fragments of the far left but, in the dealings I have had with the ISO, I have never encountered anything that could be called cult-like behaviour.