It's hard to say Jim. There's a long history of Left Zionism as well as anti-Zionism. The anti-Zionism seems more a reaction to Israel's actions against the Palestinians than a principled objection to the existence of a Jewish homeland though. Left Zionism often has had a more inclusive outlook than one might guess by the term 'Zionism' alone - and at one point there was quite a strong Left-Zionist movement who sought a right of residence in Palestine for Jewish people in cooperation with Palestinians.
The problem now for the Left is that criticism of Israel's action against Palestinians is so quickly conflated with anti-Jewish sentiment, following a string of pretty horrendous right-wing governments in Tel Aviv that have worked tirelessly to identify Judaism and Jewish heritage with Zionism - which also now appears to be an entirely right-led, right-leaning project.
Of course there are anti-Semites in the Labour Party, because there's anti-Semites in society. However, the issue now is that trying to quantify the extent of anti-Semitism in the Labour Party, and particularly to say that the problem of anti-Semitism in the party might not be as widespread as people might have been led to believe, is itself being cited as an example of anti-Semitism that deliberately attempts to downplay, dismiss, or minimise that kind of racism. This is what Corbyn has fallen foul of anyway.