This is just a perspective, and I may be making some strong and possibly unfair assertions, but the way I see the whole rumbling of antisemitism within the Labour party can be split into those factions who (personally) recognise the post-war state of Isreal but have an issue with Zionism, and those whose position is built on racial or religious grounds and which can appear as outright antisemitism.
Having lived in Isreal for two years, I can tell you that there's a large number of Israelis who are anti-Zionism. And whilst most of these probably support the continued occupation of the Golan Heights as a strategic defence against the provocations of Syria, as well as see areas of the West Bank as disputed territory, they have absolute disdain for the Zionists (and their backers) who have built settlements in previously controlled land such as the Gaza Strip or in the disputed territories. Such Zionists tend to be American Jewish fundamentalists. The more reasoned of Israelis, whilst wanting to ensure that their post-war agreed lands are protected, would probably find themselves aligned to the moderates within the Labour party.
But it seems to me that over the last 20 years also there is a new brand of politics in this area which is driven by a core membership that is more than simply Anti-Zionist: they don't want a state of Isreal is in any form, and their posturing and speeches most certainly come across as racist - we only have to look at our own Westminster representation to see this.
And so, as ever, what seems a perfectly fair, reasoned debate and position grounded in politics becomes deniable and deliberately closed down through the virtue-signalling and conflation of positions and beliefs, and leads to the action that Stamier had to take on the step to eradicating the party of its racist underbelly.