I think it is worth pointing out that long before October 7th people didn’t necessarily hate Jews, but did hate Israel. For the Irish there is an obvious identification with Palestinians as being occupied/controlled by a much more powerful neighbour and a personal history of violent resistance there that would lead them to support people they see as being in a similar position. Incidentally when I did History GCSE in the 90s one of the modules was The Irish Question and we had to write an essay comparing it to the what was called Arab-Israeli conflict. The London marchers chant ‘Resistance is justified when you are occupied’ as if October 7th could ever be justified.
The far left hate Israel because they are anti-West, anti-Imperialist, and will take an automatic stand with anyone who they see as also anti-West. This is why Corbyn accepts without hesitation anything put out by his ‘friends’ Hamas, suggested that the Syrians gassed themselves rather than Assad, and said that Novichok needed to be sent for examination to Russia so they could tell us whether they were responsible for the Salisbury attack. It’s why when Russia invaded Ukraine, Stop the War blamed NATO.
So they hate Israel. But Israel is the world’s only Jewish state, so it is very easy for that hatred to spill into antisemitism, particularly when antisemitism is always there and there are lots of people willing to spread it. Antisemitism is an unusual form of racism where instead of seeing the oppressed group as worse than other humans, they are seen as more powerful, and wealthier. This taps into the left’s natural aversion to wealth and power. People start going on about Zionists controlling the media and the Israel Lobby controlling the government as a gateway to the absolutely overt antisemitism which barely needs a surface scratch to find.
If Israel is set in the role of colonising oppressor then firstly it must be full of European Jews and Arab countries had nothing against Jews and no involvement in the Holocaust or their own pogroms. And then you move onto doubting and denying the Holocaust itself.
I have seen all of this on social media, including on Mumsnet.