It's not just Antizionism
It's plenty of other things too.
When we are arguing that Antizionism is Antisemitism, I at least used to fall into the trap of thinking Antizionism is the only thing associated with Antisemitism that Leftists fail to see as being inseparable from Antisemitism at least via Guilt by Association. But I've come to realize it's really not.
First there is being Anti Circumcision.
It's incredibly normal to see Leftists and even Libertarians argue for making Infant Circumcision illegal with no religious exemptions because "it's a procedure the Baby can't consent to" and I'm like "so is having the Ambilocal Cord cut".
The Medical arguments against Circumcision are all nonsense, actual studies keep showing Circumcision to be medically beneficial, that includes some benefits only useful when it's done soon after birth like how it reduces the risk of UTI.
The first time I ever read an Anti-Circumcision article it made an absurd claim then when Jews perform Circumcisions the Rabbis lick the blog off the babies circumcizer member. I instantly recognized the invocation of Blood Libel.
Just look at the scandal involving that Silent Hill Fandom Wiki Editor to see how quickly fixating on a dislike of Circumcision leads to Conspiratorial madness.
As a Gentile and a Paulian Christian, I don't believe Paul ever intended for his followers to stop Circumcising newborns. All of the allegedly Anti-Circumcision stuff in the New Testament is solely about the issue of imposing it on adult converts. In fact as a Credo-Baptist I see there being a direct link between the origins of Infant-Baptism and the abandonment of Circumcision, when you're doing Infant Circumcision what Infant Baptism is supposed to do becomes redundant. Plus most of the argument for there being a Biblical Basis for Infant Baptism is tied to the false doctrine that Baptism replaces Circumcision. The only time Paul talks about Baptism and Circumcision near each other is when talking about how for both the physical ritual is a symbol something spiritual, it is absolutely not saying one replaces the other.
The other issue I want to talk about is Marcionism.
People who literally believe in the fullness of Marcionite of Gnostic Theology are a niche minority. But they do exist, I sometimes watch a YouTube video made by one, and in one the Gnostic said "you know YHWH is a bad due because he loves Blood, the bloody bloody blood" once again people can't stop themselves from evoking Blood Libel.
However mild Marcionism is way more common then you think. Whenever an Atheist specifically uses the name YHWH for the God they view as Evil. Whenever Christians God acted differently in the "Old Testament".
The gist of the Marcionite way of thinking about The Bible is pretty mainstream actually.
And it amazes me how many alleged enemies of Bigotry don't see the Antisemitism in making that association. If you normalize associating everything you think is Bad about Religion with The Hebrew Bible and think all the Good Stuff doesn't show up till Jesus. Then of course many are going to conclude that those who reject Jesus and following just The Hebrew Bible must be following the most Evil Religion imaginable.