grinkle - not sure your "argument from authority" (ie Lisalisa knows best) really helps with the thread. I am one of those newbies, and to be really upfront, open and honest I am a left winger who has joined Labour recently. But I think the areas of discussion are:
Are there anti-Semitic people in the Labour Party?
Do they hold sway over the Labour Party / left wing more generally?
Does it therefore follow that the Labour Party has a problem with anti-Semitism?
If so, is it doing enough? If not, is it doing enough about individual members?
If not, is there another reason for the left wing / Labour party being painted as anti-Semitic?
Should this racism (cos lets be fair, that's exactly what being anti-Semitic is) and the issues it causes be compared to problems other parties / wings might have or dealt with in a vacuum?
Answering one of those questions for newbies as a fait accompli doesn't seem to follow logically from any of the arguments directly.