It is unclear how much of his political activities were grounded in Arab nationalism and anti-colonialism, and how much in anti-Semitism. The Arab nationalism and anti-colonialism are understandable responses to the British Empire and Jewish settlement in Palestine; the anti-Semitism is unforgivable.
Anti-Semitism is the view that originated in Germany in the 19th century that Jews are a racial group of non-European origin, and as such, don't deserve the same rights as "real" white people. It doesn't make sense to suggest that a Palestinian Arab might even have such a view. Of course a Palestinan Arab might well hate all Jews, but not for this reason. Now if you're using "anti-Semitism" as a catchall term for all anti-Jewish hostility, how can you call one form of it "understandable" and another form of it "unforgivable"? A lot of people who lived in Europe during WW2 are anti-German as a result of that experience, but who's going to wag a finger at them and say that although anti-German sentiment is an understandable response to German invasion and genocide, anti-German sentiment that comes from anti-Teutonism is unforgivable?
That said, it is important to remember that there never was a Nazi party in historic Palestine
How could there have been? Unlike, say, a Communist party, a precondition for the existence of a National Socialist party would be an already established state that could exert military power. Palestine was governed as a colony, and correct me if I'm wrong, but no colony anywhere had a Nazi party.
and that Islam does not have the centuries old history of Jew hatred that is found in European Christianity.
My understanding is that Jew-hatred such as it has been in the Islamic world is all about religious difference, never about racial difference. If you were a member of the Ummah, it didn't matter if you had Jewish ancestry.
The October issue of Harper's has a ridiculous article by Tanya Gold, "Among Britain’s Anti-Semites: The Labour Party’s Moral Dilemma":
Here's one lowlight:
Corbyn is also a patron of the Palestine Solidarity Campaign and a former chair of Stop the War, at whose rallies they chant, “From the river to the sea / Palestine will be free.” (There is no rhyme for what will happen to the Jewish population in this paradise.) He was an early supporter of the Boycott, Divestment, and Sanctions (BDS) movement and its global campaign to delegitimize Israel and, through the right of return for Palestinians, end its existence as a Jewish state.
She meets members of Jewish Voice for Labour and reports:
Of an endgame in Israel/Palestine I was told only of a vague desire for a “rainbow nation,” as if demonic can be a color in a rainbow.
And then there's this:
I am fascinated by Jackie Walker, the daughter of a Jamaican mother of Jewish descent and a Jewish-American father, and a committed anti-Zionist. ... we had long, agonized conversations about anti-Semitism and Israel. She told me, as she did the first time I met her, in 2016, that Israel is a racist state. I am keen to understand Walker. Perhaps it is because that even among a tribe of outsiders, her status is peculiarly isolated, and she is terribly abused by some Zionist Jews. Perhaps I cannot let her go, let her stop being Jewish, stop being my cousin; let her carry the burden, too! To me she is warm and emotional, and I came to like her very much, even if I felt that she couldn’t hear me: sometimes I wondered whether she is just another narcissistic and intractable Jewish female, like so many I have loved.
How is that for lack of self-awareness?
Have you noticed that people who spout anti-Palestinian propaganda never say that some of their best friends are Palestinian? The only evidence that Tanya Gold gives to show that she's ever listened to anything any Palestinian has ever said is this:
Conspiracy theories are fashionable in these ponds. A Palestinian newspaper has reported that Zionists employed a dolphin to spy on Hamas.