In his head, Corbyn believes so strongly that he can't possibly be anti-semitic that any accusation must be a politically motivated personal attack. So he can sit silent and do nothing when Mark Wadsworth abuses Ruth Smeeth or Willemson goes off on an angry rant about Jews making up instances of AS, because Wadsworth and Willemson are his friends and are speaking in his defence. He doesn't hear them being AS. All he hears is them sticking up for him.
His problem with AS is that he defines it in pre-war terms. Shylock, Fagin and the Holocaust. His obsession with the Palestinian cause and right to 'reclaim their land' makes it impossible to see anything from Israel's point of view. Justice for Palestine means returning to the status quo existing before the foundation of the Sate of Israel. The 1967 War on Israel by its Arab neighbours was a just war. Israel's annexation of territory to ensure defensible borders, e.g. the Golan Heights, wasn't defensive. It was Zionist colonial aggression.
The idea that 6 million Jews killed in the Holocaust is any sort of justification for a Jewish homeland is a bit tricky. After all Palestine was a Jewish state for thousands of years before they were driven out. Palestine has never existed as a Palestinian state. The solution in his circles seems to be to minimise the Holocaust or water it down so it wasn't a Jewish thing. Corbyn and McDonnell put up an early-day motion to change the name of Holocaust Memorial Day to Genocide Day. Jackie Walker talks about the African Holocaust and wants to call THE Holocaust by a different name.
Israel is the enemy in Corbyn's eyes. It's very existence is a hostile act. Anyone who disagrees with him is also the enemy. Understandably, there's a lot of opposition to this line of thought from Jews. (Not just from Jews, I'm glad to say.) Incrementably, they've become the enemy, too. But Corbyn? Anti-semitic? Ridiculous idea. Not a racist bone in his body, blah, blah, blah.
This isn't going to go away. If I were Jewish, I'd be a lot more worried about Corbyn than the odd Troy dinosaur trying to keep me out of the golf club.