I commented on this before:
The thing with calling the far left "antisemitic", is of course they are going to defend themselves that they, "are just being critical of Israel's oppression and no government should be above criticism".
And of course, in theory, it's a true point that you should be able to be critical of any government. But then people are going to reply along the lines that obsessing over the world's only Jewish state, and basically wanting to see it destroyed, and sympathising with the lunatic terrorists of Hamas, does look kind of suspicious as antisemitism anyway.
(End of quote)
You can compare with the accusation of "Islamophobia / racism" made against people on the harder right, or sometimes against atheist liberals.
In that case, people defend by saying that it's a criticism of ideology, and all ideology should be open to criticism. So it's not "racist" or a "phobia" to attack an ideology that has harmful consequences.
But then people may respond that it's an unfair attack on a religious group that is really motivated by a disguised bigotry.
So it does get a little complex, and depend on your perspective, whether you see something as "real racism" or not.
With Israel, maybe you take into account things like: are people using a double standard? Are they spreading misinformation? Are they marching with people that want to see Israel destroyed? Are they getting into conspiracy theories?