she Chakrabarti) has said that Antisemitism is "a serious issue"
I never said she did.
The NEC said it was "a serious issue" according to Labour List.

Sadiq Khan has not said their is a problem other than the row that has blown up might have affected his election as mayor - as your quote says ""If somebody is saying views that are appalling, disgusting and clearly anti-Semitic, I've got to call it out.", which is quite right

Yes it is quite right, and he accused Corbyn of failing to call out antisemitism in Labour.

"Former Scottish Labour leader, Jim Murphy" - is an extremist right winger

Rubbish. How can a lifelong Labour activist be "an extremist right winger?"
That is a ludicrous assertion. Ridiculous.

and a member of several pro-Israeli organisations.

So what?
Lots of people, left and right wing and from all parties, are "pro-Israel."
They are still allowed to object to anti-semitism.