Of course the poster with the quotation from Noam Chomsky is also as weasely as the souces they condemn.
No one has accused Corbyn of being pro-racist, and to his credit, I do not think he is. But he has been pro-Palestinian, which means opposed to Israel's policies in relation to Palestine. Aagain many people not in the Labour party are opposed to Israel's policies in that area.
But, as this thread has shown, the boundary between being opposed to the policies of the Israeli government and anti-Semitism is wafer thin and there were those in Corbyns inner office who were unable to see that there was a dividing line. and, as recent biographies have shown, Corbyn is a man who does not like to confront people or make decisions and so he chose to take no action against anyone close to him who was eliding opposition to Israel with anti-semitism.
You do not have to espouse a policy to be complicit in it. Corbyn is anti-semitic, not because he did or said anything anti-semitic himself, but because, when faced with it in others, including people very close to him he failed to confront it and deal with it.