The current anti-Semitism scandal that has engulfed the British Labour Party and its leader Jeremy Corbyn has finally brought out into the open a particularly nasty trait of the political left-wing - its willingness to compromise any principles it may once have held to advance its cause of cultural relativism and identity politics.
Conservative US writer Jonah Goldberg in his book Liberal Fascism wrote about how modern so-called liberal politics has common roots with Fascism and Nazism due to its origins in the late-19th/early-20th Century progressivism. The early progressives believed in 'scientific racism' and eugenics, which found their way not only into the writings of Adolf Hitler and but also into the policies of progressive US presidents Theodore Roosevelt and Woodrow Wilson. The liberal left today likes to make out that it is antithetical to racism but you only have to go back a few decades to find prominent left-of-centre politicians who were openly racist (e.g. 1972 US Democratic Party presidential candidate George Wallace was a supporter of race segregation policies).
The reason for the current anti-Semitism in the British Labour Party has more recent and prosaic origins - the rise of Islam in modern day Britain. In northern cities like Bradford and London suburbs like Tower Hamlets, the population is increasingly Muslim - and often it is a fundamentalist version of Islam that is practised by the adherents of that faith in their enclaves. You cannot be elected in these areas without being at least anti-Israel and preferably anti-Semitic to boot. The left-wing is fond of explaining that there is a difference between being anti-Israeli and being anti-Semitic and while I agree that is true in theory, in practice it is a distinction that is increasingly hard to make.
The left-wing portrays anyone who warns against the advance of Islam as racist, but of course Muslims are not a race at all but rather adherents of a religion or, more precisely, a theocratic political philosophy. It is a philosophy that is antithetical to Western values such as individual rights, freedom of speech and equality of opportunity, but it is not confined to one particular racial or ethnic group and there is nothing racist about opposing such a philosophy. Jews, on the other hand, are a race in the sense that they almost all share a relatively recent genetic origin (e.g. see this Wikipedia article for information about scientific studies of Jewish genetic ancestry).
I am not a Zionist. I do not believe that Jewish people have any a priori claim on the land that is now the State of Israel or any of its neighbouring territories. However, I do think that Israel has a right to peaceful existence by virtue of the fact that it is (for the most part) a non-aggressive, rights-respecting, democratic state (and, in fact, it is pretty much the only country in the Middle East that has these characteristics).
Left-wingers are the first to promote the cause of indigenous people as part of their identity group grievance-mongering. The fact is that the Jewish people are as close to indigenous to the area of modern Israel as any endemic people anywhere in the world. Other than a few decades in the 1st Century A.D. when the Romans expelled most Jews from what was then called Palestine, there have been ancestors of today's Jewish people in that area since antiquity (and you don't need to buy the whole Moses and twelve tribes mythology to accept this historical fact). So left-wingers who oppose Israel are hypocritical at best.
I believe everyone is entitled to their beliefs and to express those beliefs but I also detest those who for political reasons judge people, favourably or negatively, on the basis of some inherent group trait. The identity politics of the left-wing does precisely that. It is 'groupism' (which incidentally is a literal translation of 'Fascism') and when it comes from the hypocritical left-wing, it is particularly abhorrent.