His critics homed in on Jewdas' anti-Israel views, and accused Corbyn of "baiting mainstream Jews".
Mr Lansman replied: "I think we all should".
He added that "anti-Semitism is a vile and evil thing" and Labour had a process for dealing with it. Corbyn said that the event gave him a chance to celebrate the holiday "with young Jewish people from my own community".
Mr Corbyn attended a Seder event, the Jewish Feast Day that marks the start of Passover, on Monday with members of the group in a personal capacity, according to his spokesman.
Jewish Labour Movement said in a statement that Corbyn had "truly topped off the worst week on record of terrible relations between the Labour Party and the Jewish community".
"Jeremy Corbyn is a man of his political era and hasn't got the intellectual flexibility to move on from that, and to question some of his views", Professor Fielding said.
It also followed a statement by the left-wing Momentum group which declaredanti-Semitism was more widespread in Labour than was thought and complaints could not be dismissed as right-wing smears.
The Jewish Labour Movement, who has already criticized Corbyn's relations with the Jewish community, said the Labour leader's presence at the event "topped off the worst week on record of terrible relations between the Labour Party and the Jewish community". "Isn't that a good thing?"
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After the Seder, Jewdas tweeted that "tonight reminded us that the reasons we're Jewish are the same as our reasons for being revolutionaries: our commitment to making this world better than it is now".
The spokesman also noted that Corbyn "wrote to the Board of Deputies and Jewish Leadership Council last week to ask for an urgent formal meeting to discuss tackling antisemitism in the Labour party and in society".
We conclude that he can not seriously contemplate anti-Semitism, because he is so ideologically fixed within a far left worldview that is instinctively hostile to mainstream Jewish communities.
Sir David claimed Labour's "constant protestations that they will not tolerate anti-Semitism" within the party are "so blatantly countered in reality by their failure to expel Labour Party members who have engaged in the most ugly and grotesque accusations and characterisations and the kind of fantasies that became all too common in the '30s in Germany".
Commenting on the row, Sir David told Sky News the group "does not represent the Jewish community in the country", adding: "They are a fringe group, motivated by their hatred of the State of Israel".
Karen Pollock, the chief executive of the Holocaust Educational Trust, claimed that Corbyn's meeting was "clearly deliberate".
Jon Lansman, founder of the Corbyn-supporting Momentum group, said the Labour leader had not told his own office he was going to the event.
Jewdas responded to the criticism on Twitter, posting: "This has been a hard week to be a lefty Jew".