Mehdi Hasan @mehdirhassan is doing two things here.
He says that comparing Israel to Nazis is wrong/inaccurate/offensive but not antisemitic.
We often see this pleading guilty to a lesser crime.
Livingstone is said to be vulgar or insensitive but not antisemitic.
Antisemitism is taboo and there is resistance to accepting its existence.
But this bullying was not antisemitic? Again, guilty to a lesser charge.
When it's offensive, who is it offending?
When there is loud mouthed bullying, who is being bullied?
And why?
What is the wider political context - and outcome - of the inaccuracy, offending and bullying?
And then, instead of denials and counter-accusations, the left would have to make judgments about particular cases.
And to educate the young about antisemitism.
There is bullying, over-enthusiasm, getting things wrong but not antisemitism. And then those who say there's a problem of antisemitism can be pushed out of the community of the good and treated as enemies.
The second issue is that the IHRA definition can really help with @mehdirhasan's question.
IHRA doesn't say that comparing Israel to Nazis is antisemitic.
"Drawing comparisons of contemporary Israeli policy to that of the Nazis."
IHRA says, therefore, that when Meyer or Kaufman compare Israel to Nazis, then you have to think about that.
Think about its meaning.
Think about intent.
Think about effect.
Think about whether it bullies Jews, or it libels Jews or it is offensive to Jews.
And then make a judgement about whether it is antisemitic.
It says specifically to Jews that what they are doing makes them comparable to those who herded hundreds of thousands of their own children into the gas.
So denouncing Israel as Nazi has the effect of educating people to assume that Jews they meet are like Nazis; and should be treated as Nazis.
Unless they disavow Israel.